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Reviewed-by: Pruthi, Vineet <vineet.pruthi@t-systems.com>
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<a name="EN-US_TOPIC_0000001811515441"></a><a name="EN-US_TOPIC_0000001811515441"></a>
<h1 class="topictitle1">UNION, CASE, and Related Constructs</h1>
<div id="body8662426"><p id="EN-US_TOPIC_0000001811515441__en-us_topic_0059779260_p269514716590">SQL UNION constructs must match up possibly dissimilar types to become a single result set. Since all query results from a <strong id="EN-US_TOPIC_0000001811515441__b44504733933556">SELECT UNION</strong> statement must appear in a single set of columns, the types of the results of each <strong id="EN-US_TOPIC_0000001811515441__b5554435133556">SELECT</strong> clause must be matched up and converted to a uniform set. Similarly, the result expressions of a <strong id="EN-US_TOPIC_0000001811515441__b159580920333556">CASE</strong> construct must be converted to a common type so that the <strong id="EN-US_TOPIC_0000001811515441__b177841883433556">CASE</strong> expression as a whole has a known output type. The same holds for <strong id="EN-US_TOPIC_0000001811515441__b171744690033556">ARRAY</strong> constructs, and for the <strong id="EN-US_TOPIC_0000001811515441__b164854960733556">GREATEST</strong> and <strong id="EN-US_TOPIC_0000001811515441__b142796099633556">LEAST</strong> functions.</p>
<div class="section" id="EN-US_TOPIC_0000001811515441__s5c81516e10974f338b4b7d772d38f497"><h4 class="sectiontitle">Type Resolution for UNION, CASE, and Related Constructs</h4><ul id="EN-US_TOPIC_0000001811515441__u7d71a8ec8a4e4cd49be14956f188a959"><li id="EN-US_TOPIC_0000001811515441__l57f75649247c4f549873fd156157b8cc">If all inputs are of the same type, and it is not unknown, resolve as that type.</li><li id="EN-US_TOPIC_0000001811515441__la0d1d70a218b4404b7271bcaf313075c">If all inputs are of type <strong id="EN-US_TOPIC_0000001811515441__b84235270692017">unknown</strong>, resolve as type <strong id="EN-US_TOPIC_0000001811515441__b84235270692024">text</strong> (the preferred type of the string category). Otherwise, <strong id="EN-US_TOPIC_0000001811515441__b84235270692044">unknown</strong> inputs are ignored.</li><li id="EN-US_TOPIC_0000001811515441__lce61619a8b6b4625b83cef42fce78007">If the entered values are not the same type, the query fails (except for the <strong id="EN-US_TOPIC_0000001811515441__b1839814281833">unknown</strong> type).</li><li id="EN-US_TOPIC_0000001811515441__la1cbb755423441f29b266716414b9875">When input types fall under the same category, the preferred type of that category is chosen, unless the union operation selects the type of the first branch as the chosen type.<div class="note" id="EN-US_TOPIC_0000001811515441__n48be18a738e1417baf129c38c36671e2"><img src="public_sys-resources/note_3.0-en-us.png"><span class="notetitle"> </span><div class="notebody"><p id="EN-US_TOPIC_0000001811515441__acd09fdbd7dbb48fd9c16e6fe33fe54cc"><strong id="EN-US_TOPIC_0000001811515441__b842352706171247">typcategory</strong> in the <strong id="EN-US_TOPIC_0000001811515441__b842352706171237">pg_type</strong> system catalog indicates the data type category. <strong id="EN-US_TOPIC_0000001811515441__b84235270617134">typispreferred</strong> indicates whether a type is preferred in <strong id="EN-US_TOPIC_0000001811515441__b842352706171348">typcategory</strong>.</p>
</div></div>
</li><li id="EN-US_TOPIC_0000001811515441__la520dfab50e441e4b8cd81def938de73">All the input is converted to the selected type. (The original length of a string is retained). Fail if there is not an implicit conversion from a given input to the selected type.</li><li id="EN-US_TOPIC_0000001811515441__li17401536195716">If the input contains the json, txid_snapshot, sys_refcursor, or geometry type, <strong id="EN-US_TOPIC_0000001811515441__b3356338519">UNION</strong> cannot be performed.</li></ul>
</div>
<div class="section" id="EN-US_TOPIC_0000001811515441__s6c7bfb5b733c473bbdc05fb34f856021"><h4 class="sectiontitle">Type Resolution for CASE, COALESCE, IF, and IFNULL in TD-Compatible Mode</h4><ul id="EN-US_TOPIC_0000001811515441__uc41f3b659cfa40c59e8397fca7f459cf"><li id="EN-US_TOPIC_0000001811515441__l33cf764b60a04d6db5003c59bead82a8">If all inputs are of the same type, and it is not unknown, resolve as that type.</li><li id="EN-US_TOPIC_0000001811515441__l98abad52c35d4aab8c48a106aa53dcf8">If all inputs are of type <strong id="EN-US_TOPIC_0000001811515441__b71365099919436">unknown</strong>, resolve as type <strong id="EN-US_TOPIC_0000001811515441__b87930857019436">text</strong>.</li><li id="EN-US_TOPIC_0000001811515441__l923249e8d12840659a1c9ca94503359e">If inputs are of string type (including <strong id="EN-US_TOPIC_0000001811515441__b842352706192652">unknown</strong> which is resolved as type <strong id="EN-US_TOPIC_0000001811515441__b842352706192729">text</strong>) and digit type, resolve as the string type. If the inputs are not of the two types, fail.</li><li id="EN-US_TOPIC_0000001811515441__l0561594b643746ea9ff7b49265fe4f21">If the non-unknown inputs are all of the same type category, choose the input type which is a preferred type in that category, if there is one.</li><li id="EN-US_TOPIC_0000001811515441__lb761861c355247109ca3b81846417cde">Convert all inputs to the selected type. Fail if there is not an implicit conversion from a given input to the selected type.</li></ul>
</div>
<div class="section" id="EN-US_TOPIC_0000001811515441__section1421264504414"><h4 class="sectiontitle">Type Resolution for CASE, COALESCE, IF, and IFNULL in MySQL-Compatible Mode</h4><ul id="EN-US_TOPIC_0000001811515441__ul219416462448"><li id="EN-US_TOPIC_0000001811515441__li41947466445">If all inputs are of the same type, and it is not unknown, resolve as that type.</li><li id="EN-US_TOPIC_0000001811515441__li1919414614446">If all inputs are of type <strong id="EN-US_TOPIC_0000001811515441__b1040438442">unknown</strong>, resolve as type <strong id="EN-US_TOPIC_0000001811515441__b1913211397">text</strong>.</li><li id="EN-US_TOPIC_0000001811515441__li998614192154">If some inputs are of type <strong id="EN-US_TOPIC_0000001811515441__b56046393912">unknown</strong> and the others are of a non-<strong id="EN-US_TOPIC_0000001811515441__b09617174224">unknown</strong> type, resolve as that non-<strong id="EN-US_TOPIC_0000001811515441__b059572202219">unknown</strong> type.</li><li id="EN-US_TOPIC_0000001811515441__li4277512162016">If the inputs are of different non-<strong id="EN-US_TOPIC_0000001811515441__b195101231112212">unknown</strong> types, treat type <strong id="EN-US_TOPIC_0000001811515441__b4438106143513">enum</strong> as type <strong id="EN-US_TOPIC_0000001811515441__b14396429153517">text</strong> for comparison.</li><li id="EN-US_TOPIC_0000001811515441__li19194204614416">If the non-<strong id="EN-US_TOPIC_0000001811515441__b1720813520223">unknown</strong> inputs are all of the same type, choose a preferred type, if there is one. If the inputs are of different types, resolve as type <strong id="EN-US_TOPIC_0000001811515441__b118295527412">text</strong>.</li><li id="EN-US_TOPIC_0000001811515441__li181941146154418">Convert all inputs to the selected type. Fail if there is not an implicit conversion from a given input to the selected type.</li></ul>
</div>
<div class="section" id="EN-US_TOPIC_0000001811515441__s64d7c742a50c4e00b2291bb2117d754e"><h4 class="sectiontitle">Examples</h4><p id="EN-US_TOPIC_0000001811515441__a987902d9630d45b1b58f0d4dd02acdfe">Example 1: Use type resolution with unknown types in a union as the first example. Here, the unknown-type literal <strong id="EN-US_TOPIC_0000001811515441__b8423527069274">'b'</strong> will be resolved to type <strong id="EN-US_TOPIC_0000001811515441__b84235270692718">text</strong>.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001811515441__s1512f3e03cdb4cc4b6bf521ea25f5a29"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span>
<span class="normal">6</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="nb">text</span><span class="w"> </span><span class="s1">'a'</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="ss">&quot;text&quot;</span><span class="w"> </span><span class="k">UNION</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="s1">'b'</span><span class="p">;</span>
<span class="w"> </span><span class="nb">text</span>
<span class="c1">------</span>
<span class="w"> </span><span class="n">a</span>
<span class="w"> </span><span class="n">b</span>
<span class="p">(</span><span class="mi">2</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001811515441__ad5df48e6c8ae4455830eaf089e388206">Example 2: Use type resolution in a simple union as the second example. The literal <strong id="EN-US_TOPIC_0000001811515441__b84235270692828">1.2</strong> is of type <strong id="EN-US_TOPIC_0000001811515441__b84235270692840">numeric</strong>, and the <strong id="EN-US_TOPIC_0000001811515441__b84235270692845">integer</strong> value <strong id="EN-US_TOPIC_0000001811515441__b84235270692851">1</strong> can be cast implicitly to <strong id="EN-US_TOPIC_0000001811515441__b84235270692857">numeric</strong>, so that type is used.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001811515441__sa5d4159da4114e189cc601710930416a"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span>
<span class="normal">6</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="ss">&quot;numeric&quot;</span><span class="w"> </span><span class="k">UNION</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
<span class="w"> </span><span class="nb">numeric</span>
<span class="c1">---------</span>
<span class="w"> </span><span class="mi">1</span>
<span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="mi">2</span>
<span class="p">(</span><span class="mi">2</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001811515441__a5b259cdb95a34ef58a4a66583ce09ea5">Example 3: Use type resolution in a transposed union as the third example. Here, since type <strong id="EN-US_TOPIC_0000001811515441__b105175991233556">real</strong> cannot be implicitly cast to <strong id="EN-US_TOPIC_0000001811515441__b99875165533556">integer</strong>, but <strong id="EN-US_TOPIC_0000001811515441__b108277227833556">integer</strong> can be implicitly cast to <strong id="EN-US_TOPIC_0000001811515441__b49281932133556">real</strong>, the union result type is resolved as <strong id="EN-US_TOPIC_0000001811515441__b67083371133556">real</strong>.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001811515441__s6bd7cbf9528b49368b7f1db40a75e970"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
<span class="normal">2</span>
<span class="normal">3</span>
<span class="normal">4</span>
<span class="normal">5</span>
<span class="normal">6</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="ss">&quot;real&quot;</span><span class="w"> </span><span class="k">UNION</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="k">CAST</span><span class="p">(</span><span class="s1">'2.2'</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="nb">REAL</span><span class="p">);</span>
<span class="w"> </span><span class="nb">real</span>
<span class="c1">------</span>
<span class="w"> </span><span class="mi">1</span>
<span class="w"> </span><span class="mi">2</span><span class="p">.</span><span class="mi">2</span>
<span class="p">(</span><span class="mi">2</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
</pre></div></td></tr></table></div>
</div>
<p id="EN-US_TOPIC_0000001811515441__p6335859183416">Example 4: Use type resolution in the <strong id="EN-US_TOPIC_0000001811515441__b0426144292512">COALESCE</strong> function with input values of types <strong id="EN-US_TOPIC_0000001811515441__b129251415112618">int</strong> and <strong id="EN-US_TOPIC_0000001811515441__b59210594255">varchar</strong> as the fourth example. Type resolution fails in ORA-compatible mode. The types are resolved as type <strong id="EN-US_TOPIC_0000001811515441__b1010416118296">varchar</strong> in TD-compatible mode, and as type <strong id="EN-US_TOPIC_0000001811515441__b248191320294">text</strong> in MySQL-compatible mode.</p>
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001811515441__screen1670155193519"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
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<span class="normal">76</span></pre></div></td><td class="code"><div><pre><span></span><span class="c1">-- Create the ora_db, td_db, and mysql_db databases by setting dbcompatibility to ORA, TD, and MySQL, respectively:</span>
<span class="k">CREATE</span><span class="w"> </span><span class="k">DATABASE</span><span class="w"> </span><span class="n">ora_db</span><span class="w"> </span><span class="n">dbcompatibility</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'ORA'</span><span class="p">;</span>
<span class="k">CREATE</span><span class="w"> </span><span class="k">DATABASE</span><span class="w"> </span><span class="n">td_db</span><span class="w"> </span><span class="n">dbcompatibility</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'TD'</span><span class="p">;</span>
<span class="k">CREATE</span><span class="w"> </span><span class="k">DATABASE</span><span class="w"> </span><span class="n">mysql_db</span><span class="w"> </span><span class="n">dbcompatibility</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s1">'MySQL'</span><span class="p">;</span>
<span class="c1">-- Switch to the ora_db database:</span>
<span class="err">\</span><span class="k">c</span><span class="w"> </span><span class="n">ora_db</span>
<span class="c1">-- Create the t1 table:</span>
<span class="n">ora_db</span><span class="o">=#</span><span class="w"> </span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">t1</span><span class="p">(</span><span class="n">a</span><span class="w"> </span><span class="nb">int</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">10</span><span class="p">));</span>
<span class="c1">-- Show the execution plan of a statement for querying the types int and varchar of input parameters for COALESCE:</span>
<span class="n">ora_db</span><span class="o">=#</span><span class="w"> </span><span class="k">EXPLAIN</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="k">coalesce</span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">t1</span><span class="p">;</span>
<span class="n">ERROR</span><span class="p">:</span><span class="w"> </span><span class="k">COALESCE</span><span class="w"> </span><span class="n">types</span><span class="w"> </span><span class="nb">integer</span><span class="w"> </span><span class="k">and</span><span class="w"> </span><span class="nb">character</span><span class="w"> </span><span class="nb">varying</span><span class="w"> </span><span class="n">cannot</span><span class="w"> </span><span class="n">be</span><span class="w"> </span><span class="n">matched</span>
<span class="n">CONTEXT</span><span class="p">:</span><span class="w"> </span><span class="n">referenced</span><span class="w"> </span><span class="k">column</span><span class="p">:</span><span class="w"> </span><span class="k">coalesce</span>
<span class="c1">-- Delete the table:</span>
<span class="n">ora_db</span><span class="o">=#</span><span class="w"> </span><span class="k">DROP</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">t1</span><span class="p">;</span>
<span class="c1">-- Switch to the td_db database:</span>
<span class="n">ora_db</span><span class="o">=#</span><span class="w"> </span><span class="err">\</span><span class="k">c</span><span class="w"> </span><span class="n">td_db</span>
<span class="c1">-- Create the t2 table:</span>
<span class="n">td_db</span><span class="o">=#</span><span class="w"> </span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">t2</span><span class="p">(</span><span class="n">a</span><span class="w"> </span><span class="nb">int</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">10</span><span class="p">));</span>
<span class="c1">-- Show the execution plan of a statement for querying the types int and varchar of input parameters for COALESCE:</span>
<span class="n">td_db</span><span class="o">=#</span><span class="w"> </span><span class="k">EXPLAIN</span><span class="w"> </span><span class="k">VERBOSE</span><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="k">coalesce</span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </span><span class="k">from</span><span class="w"> </span><span class="n">t2</span><span class="p">;</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">-----------------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">distinct</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+----------------------------------------------+--------+------------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="k">Data</span><span class="w"> </span><span class="n">Node</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="ss">&quot;__REMOTE_FQS_QUERY__&quot;</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span><span class="mi">00</span>
<span class="w"> </span><span class="n">Targetlist</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">-------------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="c1">--Data Node Scan on &quot;__REMOTE_FQS_QUERY__&quot;</span>
<span class="w"> </span><span class="k">Output</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="k">COALESCE</span><span class="p">((</span><span class="n">t2</span><span class="p">.</span><span class="n">a</span><span class="p">)::</span><span class="nb">character</span><span class="w"> </span><span class="nb">varying</span><span class="p">,</span><span class="w"> </span><span class="n">t2</span><span class="p">.</span><span class="n">b</span><span class="p">))</span>
<span class="w"> </span><span class="n">Node</span><span class="o">/</span><span class="n">s</span><span class="p">:</span><span class="w"> </span><span class="k">All</span><span class="w"> </span><span class="n">datanodes</span>
<span class="w"> </span><span class="n">Remote</span><span class="w"> </span><span class="n">query</span><span class="p">:</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="k">COALESCE</span><span class="p">(</span><span class="n">a</span><span class="p">::</span><span class="nb">character</span><span class="w"> </span><span class="nb">varying</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="ss">&quot;coalesce&quot;</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="k">public</span><span class="p">.</span><span class="n">t2</span>
<span class="p">(</span><span class="mi">10</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="c1">-- Delete the table:</span>
<span class="n">td_db</span><span class="o">=#</span><span class="w"> </span><span class="k">DROP</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">t2</span><span class="p">;</span>
<span class="c1">-- Switch to the mysql_db database:</span>
<span class="n">td_db</span><span class="o">=#</span><span class="w"> </span><span class="err">\</span><span class="k">c</span><span class="w"> </span><span class="n">mysql_db</span>
<span class="c1">-- Create the t3 table:</span>
<span class="n">mysql_db</span><span class="o">=#</span><span class="w"> </span><span class="k">CREATE</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">t3</span><span class="p">(</span><span class="n">a</span><span class="w"> </span><span class="nb">int</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="nb">varchar</span><span class="p">(</span><span class="mi">10</span><span class="p">));</span>
<span class="c1">-- Show the execution plan of a statement for querying the types int and varchar of input parameters for COALESCE:</span>
<span class="n">mysql_db</span><span class="o">=#</span><span class="w"> </span><span class="k">EXPLAIN</span><span class="w"> </span><span class="k">VERBOSE</span><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="k">coalesce</span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </span><span class="k">from</span><span class="w"> </span><span class="n">t3</span><span class="p">;</span>
<span class="w"> </span><span class="n">QUERY</span><span class="w"> </span><span class="n">PLAN</span>
<span class="c1">-----------------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="k">operation</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">rows</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="k">distinct</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">width</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">E</span><span class="o">-</span><span class="n">costs</span>
<span class="w"> </span><span class="c1">----+----------------------------------------------+--------+------------+---------+---------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">-&gt;</span><span class="w"> </span><span class="k">Data</span><span class="w"> </span><span class="n">Node</span><span class="w"> </span><span class="n">Scan</span><span class="w"> </span><span class="k">on</span><span class="w"> </span><span class="ss">&quot;__REMOTE_FQS_QUERY__&quot;</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span><span class="mi">00</span>
<span class="w"> </span><span class="n">Targetlist</span><span class="w"> </span><span class="n">Information</span><span class="w"> </span><span class="p">(</span><span class="n">identified</span><span class="w"> </span><span class="k">by</span><span class="w"> </span><span class="n">plan</span><span class="w"> </span><span class="n">id</span><span class="p">)</span>
<span class="w"> </span><span class="c1">------------------------------------------------------------------------------------</span>
<span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="c1">--Data Node Scan on &quot;__REMOTE_FQS_QUERY__&quot;</span>
<span class="w"> </span><span class="k">Output</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="k">COALESCE</span><span class="p">((</span><span class="n">t3</span><span class="p">.</span><span class="n">a</span><span class="p">)::</span><span class="nb">text</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="n">t3</span><span class="p">.</span><span class="n">b</span><span class="p">)::</span><span class="nb">text</span><span class="p">))</span>
<span class="w"> </span><span class="n">Node</span><span class="o">/</span><span class="n">s</span><span class="p">:</span><span class="w"> </span><span class="k">All</span><span class="w"> </span><span class="n">datanodes</span>
<span class="w"> </span><span class="n">Remote</span><span class="w"> </span><span class="n">query</span><span class="p">:</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="k">COALESCE</span><span class="p">(</span><span class="n">a</span><span class="p">::</span><span class="nb">text</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">::</span><span class="nb">text</span><span class="p">)</span><span class="w"> </span><span class="k">AS</span><span class="w"> </span><span class="ss">&quot;coalesce&quot;</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="k">public</span><span class="p">.</span><span class="n">t3</span>
<span class="p">(</span><span class="mi">10</span><span class="w"> </span><span class="k">rows</span><span class="p">)</span>
<span class="c1">-- Delete the table:</span>
<span class="n">mysql_db</span><span class="o">=#</span><span class="w"> </span><span class="k">DROP</span><span class="w"> </span><span class="k">TABLE</span><span class="w"> </span><span class="n">t3</span><span class="p">;</span>
<span class="c1">-- Switch to the gaussdb database.</span>
<span class="n">mysql_db</span><span class="o">=#</span><span class="w"> </span><span class="err">\</span><span class="k">c</span><span class="w"> </span><span class="n">gaussdb</span>
<span class="c1">-- Delete the databases:</span>
<span class="k">DROP</span><span class="w"> </span><span class="k">DATABASE</span><span class="w"> </span><span class="n">ora_db</span><span class="p">;</span>
<span class="k">DROP</span><span class="w"> </span><span class="k">DATABASE</span><span class="w"> </span><span class="n">td_db</span><span class="p">;</span>
<span class="k">DROP</span><span class="w"> </span><span class="k">DATABASE</span><span class="w"> </span><span class="n">mysql_db</span><span class="p">;</span>
</pre></div></td></tr></table></div>
</div>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="dws_06_0075.html">Type Conversion</a></div>
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