EmmyMiao87 commented on a change in pull request #3135: support subquery in
case when statement
URL: https://github.com/apache/incubator-doris/pull/3135#discussion_r395417350
##########
File path: fe/src/main/java/org/apache/doris/analysis/StmtRewriter.java
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@@ -953,5 +957,81 @@ private static Expr createJoinConjunct(Expr
exprWithSubquery, InlineViewRef inli
smap.put(subquery, subquerySubstitute);
return exprWithSubquery.substitute(smap, analyzer, false);
}
+
+ /** rewrite subquery in case when to an inline view
+ * subquery in case when statement like
+ *
+ * SELECT CASE
+ * WHEN (
+ * SELECT COUNT(*) / 2
+ * FROM t
+ * ) > k4 THEN (
+ * SELECT AVG(k4)
+ * FROM t
+ * )
+ * ELSE (
+ * SELECT SUM(k4)
+ * FROM t
+ * )
+ * END AS kk4
+ * FROM t;
+ * this statement will be rewrite to
+ *
+ * SELECT CASE
+ * WHEN t1.a > k4 THEN t2.a
+ * ELSE t3.a
+ * END AS kk4
+ * FROM t, (
+ * SELECT COUNT(*) / 2 AS a
+ * FROM t
+ * ) t1, (
+ * SELECT AVG(k4) AS a
+ * FROM t
+ * ) t2, (
+ * SELECT SUM(k4) AS a
+ * FROM t
+ * ) t3;
+ */
+ private static void rewriteCaseWhenSubqueries(SelectStmt stmt, Analyzer
analyzer) throws AnalysisException {
+ for (SelectListItem item: stmt.getSelectList().getItems()) {
+ if (!(item.getExpr() instanceof CaseExpr)) {
+ continue;
+ }
+ if
(!item.getExpr().contains(Predicates.instanceOf(Subquery.class))) {
+ continue;
+ }
+ item.setExpr(rewriteCaseWhenSubquery(item.getExpr(), stmt,
analyzer));
+ }
+
+ }
+
+ private static Expr rewriteCaseWhenSubquery(Expr expr, SelectStmt stmt,
Analyzer analyzer)
+ throws AnalysisException {
+ if (expr instanceof Subquery) {
+ if (!(((Subquery) expr).getStatement() instanceof SelectStmt)) {
+ throw new AnalysisException("only support select subquery in
case statement.");
+ }
+ SelectStmt subquery = (SelectStmt) ((Subquery)
expr).getStatement();
+ if (subquery.getSelectList().getItems().size() != 1) {
Review comment:
The correlated subquery should be forbidden.
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