fix: improve COALESCE handling and jsonb_array_length compatibility

This commit addresses two issues with PostgreSQL compatibility:

1. COALESCE expression handling:
   - Recursively process all expressions in COALESCE arguments
   - Handles nested function calls within COALESCE (e.g., jsonb_array_length)
   - Previously only processed SubLink nodes, now handles all expression types

2. jsonb_array_length return type:
   - Cast result to INTEGER to match PostgreSQL's int4 return type (OID 23)
   - PostgreSQL's jsonb_array_length() returns INTEGER, not BIGINT or UBIGINT
   - Updated test expectations from XID8OID (5069) to Int4OID (23)

Tests added:
- COALESCE with JSONB types
- jsonb_array_length with COALESCE expressions

Author: JC1738

src/server/query_handler_test.go

@@ -195,7 +195,7 @@ func TestHandleQuery(t *testing.T) {
 			},
 			"SELECT jsonb_array_length('[1, 2, 3]'::jsonb)": {
 				"description": {"jsonb_array_length"},
-				"types":       {uint32ToString(pgtype.XID8OID)},
+				"types":       {uint32ToString(pgtype.Int4OID)},
 				"values":      {"3"},
 			},
 			"SELECT jsonb_pretty('{\"key\": \"value\"}'::JSONB)": {
@@ -258,6 +258,16 @@ func TestHandleQuery(t *testing.T) {
 				"types":       {uint32ToString(pgtype.TextOID)},
 				"values":      {"bemidb"},
 			},
+			"SELECT COALESCE(NULL, '[]'::jsonb) AS json_value": {
+				"description": {"json_value"},
+				"types":       {uint32ToString(pgtype.JSONOID)},
+				"values":      {"[]"},
+			},
+			"SELECT jsonb_array_length(COALESCE('[]'::jsonb, '{}'::jsonb)) AS length": {
+				"description": {"length"},
+				"types":       {uint32ToString(pgtype.Int4OID)},
+				"values":      {"0"},
+			},
 			"SELECT * FROM pg_catalog.pg_stat_gssapi": {
 				"description": {"pid", "gss_authenticated", "principal", "encrypted", "credentials_delegated"},
 				"types":       {uint32ToString(pgtype.Int4OID), uint32ToString(pgtype.BoolOID), uint32ToString(pgtype.TextOID), uint32ToString(pgtype.BoolOID), uint32ToString(pgtype.BoolOID)},

src/server/query_remapper.go

@@ -354,11 +354,9 @@ func (remapper *QueryRemapper) remappedExpressions(node *pgQuery.Node, remappedC
 	// COALESCE(value1, value2, ...)
 	coalesceExpr := node.GetCoalesceExpr()
 	if coalesceExpr != nil {
-		for _, arg := range coalesceExpr.Args {
-			if arg.GetSubLink() != nil {
-				// Nested SELECT
-				subSelect := arg.GetSubLink().Subselect.GetSelectStmt()
-				remapper.remapSelectStatement(subSelect, permissions, indentLevel+1) // recursion
+		for i, arg := range coalesceExpr.Args {
+			if arg != nil {
+				coalesceExpr.Args[i] = remapper.remappedExpressions(arg, remappedColumnRefs, permissions, indentLevel+1) // self-recursion
 			}
 		}
 	}

src/server/query_remapper_function.go

@@ -42,7 +42,7 @@ func CreatePgCatalogMacroQueries(config *Config) []string {
 			ELSE json_extract_path_text(from_json, path_elems)::varchar
 		END`,
 		`CREATE MACRO jsonb_object_agg(key, value) AS to_json(map(array_agg(key), array_agg(value)))`,
-		`CREATE MACRO jsonb_array_length(json) AS json_array_length(json)`,
+		`CREATE MACRO jsonb_array_length(json) AS CAST(json_array_length(json) AS INTEGER)`,
 		`CREATE MACRO jsonb_pretty(json) AS json_pretty(json)`,
 		`CREATE MACRO json_array_elements(json) AS unnest(json_extract(json, '$[*]'))`,
 		`CREATE MACRO jsonb_array_elements(json) AS unnest(json_extract(json, '$[*]'))`,