SELECT EXISTS(...) returns INT2 instead of BOOL, breaking typed PostgreSQL clients

[johannesdb]

Description

SELECT EXISTS(SELECT 1 FROM ...) returns a value with type INT2 (smallint) instead of BOOL, which is the correct PostgreSQL behavior. This breaks any typed PostgreSQL client that expects the standard return type.

Reproduction

-- In PostgreSQL:
SELECT EXISTS(SELECT 1 FROM pg_catalog.pg_tables WHERE tablename = 'test');
-- Returns: true (type: bool)

-- In DoltgreSQL:
SELECT EXISTS(SELECT 1 FROM pg_catalog.pg_tables WHERE tablename = 'test');
-- Returns: 1 (type: int2)

Impact

Any client library that uses typed query results will fail. For example, in Rust with SQLx:

// This works in PostgreSQL but fails in DoltgreSQL:
let exists = sqlx::query_scalar::<_, bool>(
    "SELECT EXISTS(SELECT 1 FROM users WHERE email = $1)"
)
.bind(&email)
.fetch_one(&pool)
.await?;

Error: mismatched types; Rust type boolis not compatible with SQL typeINT2``

Workaround

We currently rewrite all EXISTS queries to use COUNT(*):

-- Instead of:
SELECT EXISTS(SELECT 1 FROM users WHERE email = $1)

-- We use:
SELECT COUNT(*) FROM users WHERE email = $1
-- and then check > 0 in application code

This is a significant migration burden — in our codebase we have 22+ locations that need this workaround.

Expected behavior

SELECT EXISTS(...) should return BOOL (OID 16), matching PostgreSQL behavior.

Environment

• DoltgreSQL: latest Docker image (dolthub/doltgresql:latest)
• Client: SQLx 0.8 (Rust), but affects any typed PostgreSQL client

[Hydrocharged]

This was fixed in the linked PR.