Thanks for the patch! See 6 comments below.
And I have pushed more minor fixes on the branch. Please,
squash.
diff --git a/src/box/sql/expr.c b/src/box/sql/expr.c
index 70e134f21..23cee593f 100644
--- a/src/box/sql/expr.c
+++ b/src/box/sql/expr.c
@@ -2874,10 +2874,14 @@ sqlite3CodeSubselect(Parse * pParse, /* Parsing
context */
dest.iSDParm);
VdbeComment((v, "Init EXISTS result"));
}
- sql_expr_delete(pParse->db, pSel->pLimit, false);
- pSel->pLimit = sqlite3ExprAlloc(pParse->db, TK_INTEGER,
- &sqlite3IntTokens[1],
- 0);
+ if (pSel->pLimit == NULL) {
+ pSel->pLimit =
+ sqlite3ExprAlloc(pParse->db, TK_INTEGER,
+ &sqlite3IntTokens[1],
+ 0);
+ ExprSetProperty(pSel->pLimit, EP_System);
+ }
+ pSel->selFlags |= SF_SingleRow;
pSel->iLimit = 0;
pSel->selFlags &= ~SF_MultiValue;
if (sqlite3Select(pParse, pSel, &dest)) {
diff --git a/src/box/sql/select.c b/src/box/sql/select.c
index 54f78a9de..daec802da 100644
--- a/src/box/sql/select.c
+++ b/src/box/sql/select.c
@@ -2120,6 +2120,38 @@ computeLimitRegisters(Parse * pParse, Select * p, int
iBreak)
sqlite3VdbeAddOp2(v, OP_IfNot, iLimit, iBreak);
VdbeCoverage(v);
}
+ if (p->selFlags & SF_SingleRow) {
+ if (ExprHasProperty(p->pLimit, EP_System)) {
+ /*
+ * Indirect LIMIT 1 is allowed only for
+ * requests returning only 1 row.
+ * To test this, we change LIMIT 1 to
+ * LIMIT 2 and will look up LIMIT 1 overflow
+ * at the sqlite3Select end.
+ */
+ sqlite3VdbeAddOp2(v, OP_Integer, 2, iLimit);
+ } else {
+ /*
+ * User-defined complex limit for subquery
+ * could be only 1 as resulting value.
+ */
+ int r1 = sqlite3GetTempReg(pParse);
+ sqlite3VdbeAddOp2(v, OP_Integer, 1, r1);
+ int no_err = sqlite3VdbeMakeLabel(v);
+ sqlite3VdbeAddOp3(v, OP_Eq, iLimit, no_err, r1);
+ const char *error =
+ "Expression subquery could be limited "
+ "only with 1.";
+ sqlite3VdbeAddOp4(v, OP_Halt,
+ SQL_TARANTOOL_ERROR,
+ 0, 0, error, P4_STATIC);
+ sqlite3VdbeResolveLabel(v, no_err);
+ sqlite3ReleaseTempReg(pParse, r1);
+
+ /* Runtime checks are no longer needed. */
+ p->selFlags &= ~SF_SingleRow;
+ }
+ }
@@ -5398,6 +5430,31 @@ explain_simple_count(struct Parse *parse_context, const
char *table_name)
}
}
+/**
+ * Generate VDBE code that HALT program when subselect returned
+ * more than one row (determined as LIMIT 1 overflow).
+ * @param parser Current parsing context.
+ * @param limit_reg LIMIT register.
+ * @param end_mark mark to jump if select returned distinct one
+ * row as expected.
+ */
+static void
+vdbe_code_raise_on_multiple_rows(struct Parse *parser, int limit_reg, int
end_mark)
+{
+ assert(limit_reg != 0);
+ struct Vdbe *v = sqlite3GetVdbe(parser);
+ assert(v != NULL);
+
+ int r1 = sqlite3GetTempReg(parser);
+ sqlite3VdbeAddOp2(v, OP_Integer, 0, r1);
+ sqlite3VdbeAddOp3(v, OP_Ne, r1, end_mark, limit_reg);
+ const char *error = "Expression subquery returned more than 1 row";
+ sqlite3VdbeAddOp4(v, OP_Halt, SQL_TARANTOOL_ERROR,
+ ON_CONFLICT_ACTION_FAIL, 0,
+ error, P4_STATIC);
+ sqlite3ReleaseTempReg(parser, r1);
+}
+
/*
* Generate code for the SELECT statement given in the p argument.
*
@@ -6326,8 +6389,10 @@ sqlite3Select(Parse * pParse, /* The parser
context */
generateSortTail(pParse, p, &sSort, pEList->nExpr, pDest);
}
- /* Jump here to skip this query
- */
+ /* Generate code that prevent returning multiple rows. */
+ if (p->selFlags & SF_SingleRow && p->iLimit != 0)
+ vdbe_code_raise_on_multiple_rows(pParse, p->iLimit, iEnd);
+ /* Jump here to skip this query. */
sqlite3VdbeResolveLabel(v, iEnd);
/* The SELECT has been coded. If there is an error in the Parse structure,
diff --git a/src/box/sql/sqliteInt.h b/src/box/sql/sqliteInt.h
index e939663b6..bacf415df 100644
--- a/src/box/sql/sqliteInt.h
+++ b/src/box/sql/sqliteInt.h> @@ -2702,6 +2704,8 @@ struct Select {
#define SF_FixedLimit 0x04000 /* nSelectRow set by a constant LIMIT */
#define SF_MaybeConvert 0x08000 /* Need
convertCompoundSelectToSubquery() */
#define SF_Converted 0x10000 /* By convertCompoundSelectToSubquery()
*/
+/** Abort subquery if its output contains more than one row. */
+#define SF_SingleRow 0x40000
