sql: remove one row limit in EXISTS subquery

According to ANSI, EXISTS is a predicate that tests a given subquery and
returns true if it returns more than 0 rows, false otherwise. However,
after 2a720d1, EXISTS worked correctly only if there were exactly 0
or 1 rows, and in all other cases it gave an error. This patch makes
EXITS work properly.

Closes #8676

NO_DOC=bugfix

changelogs/unreleased/gh-8676-fix-exists-predicate.md

@@ -0,0 +1,4 @@
+## bugfix/sql
+
+* The `EXISTS` predicate no longer requires `LIMIT 1` to work correctly if more
+  than one row is returned in the subselect (gh-8676).

src/box/sql/expr.c

@@ -2774,9 +2774,6 @@ sqlCodeSubselect(Parse * pParse,	/* Parsing context */
 			 *
 			 * If this is an EXISTS, write an integer 0 (not exists) or 1 (exists)
 			 * into a register and return that register number.
-			 *
-			 * In both cases, the query is augmented with "LIMIT 1".  Any
-			 * preexisting limit is discarded in place of the new LIMIT 1.
 			 */
 			Select *pSel;	/* SELECT statement to encode */
 			SelectDest dest;	/* How to deal with SELECT result */
@@ -2802,12 +2799,22 @@ sqlCodeSubselect(Parse * pParse,	/* Parsing context */
 				sqlVdbeAddOp2(v, OP_Bool, false, dest.iSDParm);
 				VdbeComment((v, "Init EXISTS result"));
 			}
-			if (pSel->pLimit == NULL) {
-				pSel->pLimit = sql_expr_new(TK_INTEGER,
-							    &sqlIntTokens[1]);
-				ExprSetProperty(pSel->pLimit, EP_System);
+			if (pExpr->op == TK_SELECT) {
+				if (pSel->pLimit == NULL) {
+					pSel->pLimit = sql_expr_new_int(1);
+					ExprSetProperty(pSel->pLimit,
+							EP_System);
+				}
+				pSel->selFlags |= SF_SingleRow;
+			} else {
+				/*
+				 * For EXISTS it doesn't matter whether we
+				 * return one or more results, so just replace
+				 * limit with 1.
+				 */
+				sql_expr_delete(pSel->pLimit);
+				pSel->pLimit = sql_expr_new_int(1);
 			}
-			pSel->selFlags |= SF_SingleRow;
 			pSel->iLimit = 0;
 			pSel->selFlags &= ~SF_MultiValue;
 			if (sqlSelect(pParse, pSel, &dest)) {

test/sql-luatest/gh_8676_exists_in_multiselect_test.lua

@@ -0,0 +1,20 @@
+local server = require('luatest.server')
+local t = require('luatest')
+
+local g = t.group()
+
+g.before_all(function()
+    g.server = server:new({alias = 'master'})
+    g.server:start()
+end)
+
+g.after_all(function()
+    g.server:stop()
+end)
+
+g.test_exists = function()
+    g.server:exec(function()
+        local res = box.execute([[SELECT EXISTS (VALUES (1), (2));]])
+        t.assert_equals(res.rows, {{true}})
+    end)
+end

test/sql-tap/tkt1473.test.lua

@@ -199,14 +199,14 @@ test:do_execsql_test(
         -- </tkt1473-2.9>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-3.2",
     [[
         SELECT EXISTS
           (SELECT 1 FROM t1 WHERE a=1 UNION ALL SELECT 2 FROM t1 WHERE b=0)
     ]], {
         -- <tkt1473-3.2>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-3.2>
     })
 
@@ -221,36 +221,36 @@ test:do_execsql_test(
         -- </tkt1473-3.3>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-3.4",
     [[
         SELECT EXISTS
           (SELECT 1 FROM t1 WHERE a=1 UNION ALL SELECT 2 FROM t1 WHERE b=4)
     ]], {
         -- <tkt1473-3.4>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-3.4>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-3.5",
     [[
         SELECT EXISTS
           (SELECT 1 FROM t1 WHERE a=1 UNION SELECT 2 FROM t1 WHERE b=4)
     ]], {
         -- <tkt1473-3.5>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-3.5>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-3.6",
     [[
         SELECT EXISTS
           (SELECT 1 FROM t1 WHERE a=0 UNION ALL SELECT 2 FROM t1 WHERE b=4)
     ]], {
         -- <tkt1473-3.6>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-3.6>
     })
 
@@ -483,7 +483,7 @@ test:do_execsql_test(
         -- </tkt1473-4.7>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-5.3",
     [[
         SELECT EXISTS (
@@ -509,11 +509,11 @@ test:do_catchsql_test(
         )
     ]], {
         -- <tkt1473-5.3>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-5.3>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-5.4",
     [[
         SELECT EXISTS (
@@ -539,11 +539,11 @@ test:do_catchsql_test(
         )
     ]], {
         -- <tkt1473-5.4>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-5.4>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-5.5",
     [[
         SELECT EXISTS (
@@ -569,11 +569,11 @@ test:do_catchsql_test(
         )
     ]], {
         -- <tkt1473-5.5>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-5.5>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-5.6",
     [[
         SELECT EXISTS (
@@ -599,7 +599,7 @@ test:do_catchsql_test(
         )
     ]], {
         -- <tkt1473-5.6>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-5.6>
     })
 
@@ -633,7 +633,7 @@ test:do_execsql_test(
         -- </tkt1473-5.7>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-6.3",
     [[
         SELECT EXISTS (
@@ -659,11 +659,11 @@ test:do_catchsql_test(
         )
     ]], {
         -- <tkt1473-6.3>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-6.3>
     })
 
-test:do_catchsql_test(
+test:do_execsql_test(
     "tkt1473-6.4",
     [[
         SELECT EXISTS (
@@ -689,7 +689,7 @@ test:do_catchsql_test(
         )
     ]], {
         -- <tkt1473-6.4>
-        1, "Failed to execute SQL statement: Expression subquery returned more than 1 row"
+        true
         -- </tkt1473-6.4>
     })