fix: isSingleStatement add test for failing case

apps/dbagent/src/lib/targetdb/explain.test.ts

@@ -37,6 +37,11 @@ describe('isSingleStatement', () => {
       expect(isSingleStatement('SELECT * FROM schema_name.table_name;')).toBe(true);
     });
 
+    test('complex SELECT with CASE, JOIN, UNION ALL and parameterized queries', () => {
+      const complexQuery = `SELECT CASE WHEN $3 < LENGTH(CAST("public"."Post"."geoJson" AS TEXT)) THEN $4 ELSE "public"."Post"."geoJson" END AS "geoJson", CASE WHEN $5 < LENGTH(CAST("public"."Post"."runs" AS TEXT)) THEN $6 ELSE "public"."Post"."runs" END AS "runs", CASE WHEN $7 < LENGTH(CAST("public"."Post"."sprints" AS TEXT)) THEN $8 ELSE "public"."Post"."sprints" END AS "sprints" FROM "public"."Post" INNER JOIN ( (SELECT "public"."Post"."id" FROM "public"."Post" ORDER BY "public"."Post"."id" ASC LIMIT $1) UNION ALL (SELECT "public"."Post"."id" FROM "public"."Post" ORDER BY "public"."Post"."id" DESC LIMIT $2) ) AS "result" ON ("result"."id" = "public"."Post"."id")`;
+      expect(isSingleStatement(complexQuery)).toBe(true);
+    });
+
     test('complex multi-line statement with comments and quotes', () => {
       const complexQuery = `
         /* multi-line comment */

apps/dbagent/src/lib/targetdb/explain.ts

@@ -104,7 +104,11 @@ class SQLParser {
       } else if (char === '"') {
         this.parseDoubleQuotedString();
       } else if (char === '$') {
-        this.parseDollarQuotedString();
+        if (this.isDollarParameter()) {
+          this.parseDollarParameter();
+        } else {
+          this.parseDollarQuotedString();
+        }
       } else if (char === '/' && this.pos + 1 < this.len && this.input[this.pos + 1] === '*') {
         this.parseBlockComment();
       } else if (char === '-' && this.pos + 1 < this.len && this.input[this.pos + 1] === '-') {
@@ -195,6 +199,37 @@ class SQLParser {
     // Don't consume the newline, let skipWhitespace handle it
   }
 
+  private isDollarParameter(): boolean {
+    // Check if this looks like $1, $2, etc. (parameter placeholder)
+    // vs $tag$content$tag$ (dollar-quoted string)
+    if (this.pos + 1 >= this.len) {
+      return false;
+    }
+
+    let i = this.pos + 1; // Skip the $
+
+    // Check if the character after $ is a digit
+    if (!/\d/.test(this.input[i]!)) {
+      return false;
+    }
+
+    // Check if it's all digits until we hit a non-digit
+    while (i < this.len && /\d/.test(this.input[i]!)) {
+      i++;
+    }
+
+    // If the next character after digits is not $, then it's a parameter placeholder
+    return i >= this.len || this.input[i] !== '$';
+  }
+
+  private parseDollarParameter(): void {
+    this.pos++; // Skip $
+    // Skip the digits
+    while (this.pos < this.len && /\d/.test(this.input[this.pos]!)) {
+      this.pos++;
+    }
+  }
+
   private skipWhitespace(): void {
     while (this.pos < this.len && /\s/.test(this.input[this.pos]!)) {
       this.pos++;