Fix the parser to allow multiple strings one after the other (#15076)

Signed-off-by: Manan Gupta <[email protected]>

go/vt/sqlparser/ast_funcs.go

@@ -2551,6 +2551,23 @@ func IsLiteral(expr Expr) bool {
 	}
 }
 
+// AppendString appends a string to the expression provided.
+// This is intended to be used in the parser only for concatenating multiple strings together.
+func AppendString(expr Expr, in string) Expr {
+	switch node := expr.(type) {
+	case *Literal:
+		node.Val = node.Val + in
+		return node
+	case *UnaryExpr:
+		node.Expr = AppendString(node.Expr, in)
+		return node
+	case *IntroducerExpr:
+		node.Expr = AppendString(node.Expr, in)
+		return node
+	}
+	return nil
+}
+
 func (ct *ColumnType) Invisible() bool {
 	return ct.Options.Invisible != nil && *ct.Options.Invisible
 }

go/vt/sqlparser/parse_test.go

@@ -3679,6 +3679,21 @@ var (
 	}, {
 		input:  `select * from t1 where col1 like 'ks\_' and col2 = 'ks\_' and col1 like 'ks_' and col2 = 'ks_'`,
 		output: `select * from t1 where col1 like 'ks\_' and col2 = 'ks\_' and col1 like 'ks_' and col2 = 'ks_'`,
+	}, {
+		input:  "select 1 from dual where 'bac' = 'b' 'a' 'c'",
+		output: "select 1 from dual where 'bac' = 'bac'",
+	}, {
+		input:  "select 'b' 'a' 'c'",
+		output: "select 'bac' from dual",
+	}, {
+		input:  "select 1 where 'bac' = N'b' 'a' 'c'",
+		output: "select 1 from dual where 'bac' = N'bac'",
+		/*We need to ignore this test because, after the normalizer, we change the produced NChar
+		string into an introducer expression, so the vttablet will never see a NChar string */
+		ignoreNormalizerTest: true,
+	}, {
+		input:  "select _ascii 'b' 'a' 'c'",
+		output: "select _ascii 'bac' from dual",
 	}, {
 		input: `kill connection 18446744073709551615`,
 	}, {