refactor: convert plpgsql functions to SQL for inlining

CLAUDE.md

@@ -175,3 +175,27 @@ HTML output is also generated in `docs/api/html/` for local preview only.
 - Build system uses `tsort` to resolve dependency order
 - Supabase build excludes operator classes (not supported)
 - **Documentation**: All functions/types must have Doxygen comments (see Documentation Standards above)
+
+### Function Language Choice (SQL vs PL/pgSQL)
+
+Prefer `LANGUAGE SQL` over `LANGUAGE plpgsql` unless you need procedural features.
+
+| Aspect            | LANGUAGE SQL                      | LANGUAGE plpgsql        |
+|-------------------|-----------------------------------|-------------------------|
+| Inlining          | ✅ Can be inlined by planner       | ❌ Never inlined         |
+| Call overhead     | Lower (can be optimized away)     | Higher (context switch) |
+| Index performance | Better for GIN index expressions  | Worse                   |
+| Control flow      | CASE expression                   | IF/THEN/ELSE            |
+
+**Why SQL wins for simple functions:**
+
+1. **Inlining** - PostgreSQL can inline simple SQL functions into the calling query, eliminating function call overhead entirely. PL/pgSQL functions are never inlined.
+2. **Index context** - Functions used in index expressions (e.g., `CREATE INDEX ... USING GIN (eql_v2.jsonb_array(col))`) are called on every row insertion/update. Inlining matters.
+3. **Simple logic** - A CASE expression is a single statement. PL/pgSQL's procedural features aren't needed.
+
+**When PL/pgSQL is appropriate:**
+
+- Multiple statements with intermediate variables
+- Exception handling (`BEGIN...EXCEPTION...END`)
+- Complex control flow (loops, early returns)
+- Dynamic SQL (`EXECUTE`)

src/encrypted/casts.sql

@@ -15,15 +15,10 @@
 CREATE FUNCTION eql_v2.to_encrypted(data jsonb)
     RETURNS public.eql_v2_encrypted
     IMMUTABLE STRICT PARALLEL SAFE
+    LANGUAGE SQL
 AS $$
-BEGIN
-    IF data IS NULL THEN
-        RETURN NULL;
-    END IF;
-
-    RETURN ROW(data)::public.eql_v2_encrypted;
-END;
-$$ LANGUAGE plpgsql;
+    SELECT ROW(data)::public.eql_v2_encrypted;
+$$;
 
 
 --! @brief Implicit cast from JSONB to encrypted type
@@ -49,15 +44,10 @@ CREATE CAST (jsonb AS public.eql_v2_encrypted)
 CREATE FUNCTION eql_v2.to_encrypted(data text)
     RETURNS public.eql_v2_encrypted
     IMMUTABLE STRICT PARALLEL SAFE
+    LANGUAGE SQL
 AS $$
-BEGIN
-    IF data IS NULL THEN
-        RETURN NULL;
-    END IF;
-
-    RETURN eql_v2.to_encrypted(data::jsonb);
-END;
-$$ LANGUAGE plpgsql;
+    SELECT eql_v2.to_encrypted(data::jsonb);
+$$;
 
 
 --! @brief Implicit cast from text to encrypted type
@@ -84,15 +74,10 @@ CREATE CAST (text AS public.eql_v2_encrypted)
 CREATE FUNCTION eql_v2.to_jsonb(e public.eql_v2_encrypted)
     RETURNS jsonb
     IMMUTABLE STRICT PARALLEL SAFE
+    LANGUAGE SQL
 AS $$
-BEGIN
-    IF e IS NULL THEN
-        RETURN NULL;
-    END IF;
-
-    RETURN e.data;
-END;
-$$ LANGUAGE plpgsql;
+    SELECT e.data;
+$$;
 
 --! @brief Implicit cast from encrypted type to JSONB
 --!

src/encrypted/compare.sql

@@ -21,35 +21,11 @@
 CREATE FUNCTION eql_v2.compare_literal(a eql_v2_encrypted, b eql_v2_encrypted)
   RETURNS integer
   IMMUTABLE STRICT PARALLEL SAFE
+  LANGUAGE SQL
 AS $$
-  DECLARE
-    a_data jsonb;
-    b_data jsonb;
-  BEGIN
-
-    IF a IS NULL AND b IS NULL THEN
-      RETURN 0;
-    END IF;
-
-    IF a IS NULL THEN
-      RETURN -1;
-    END IF;
-
-    IF b IS NULL THEN
-      RETURN 1;
-    END IF;
-
-    a_data := a.data;
-    b_data := b.data;
-
-    IF a_data < b_data THEN
-      RETURN -1;
-    END IF;
-
-    IF a_data > b_data THEN
-      RETURN 1;
-    END IF;
-
-    RETURN 0;
-  END;
-$$ LANGUAGE plpgsql;
+    SELECT CASE
+        WHEN a.data < b.data THEN -1
+        WHEN a.data > b.data THEN 1
+        ELSE 0
+    END;
+$$;

src/encrypted/functions.sql

@@ -48,11 +48,10 @@ $$ LANGUAGE plpgsql;
 CREATE FUNCTION eql_v2.ciphertext(val eql_v2_encrypted)
   RETURNS text
   IMMUTABLE STRICT PARALLEL SAFE
+  LANGUAGE SQL
 AS $$
-	BEGIN
-    RETURN eql_v2.ciphertext(val.data);
-  END;
-$$ LANGUAGE plpgsql;
+    SELECT eql_v2.ciphertext(val.data);
+$$;
 
 --! @brief State transition function for grouped_value aggregate
 --! @internal
@@ -172,14 +171,10 @@ $$ LANGUAGE plpgsql;
 CREATE FUNCTION eql_v2.meta_data(val jsonb)
   RETURNS jsonb
   IMMUTABLE STRICT PARALLEL SAFE
+  LANGUAGE SQL
 AS $$
-	BEGIN
-     RETURN jsonb_build_object(
-      'i', val->'i',
-      'v', val->'v'
-    );
-  END;
-$$ LANGUAGE plpgsql;
+    SELECT jsonb_build_object('i', val->'i', 'v', val->'v');
+$$;
 
 --! @brief Extract metadata from encrypted column value
 --!
@@ -200,9 +195,8 @@ $$ LANGUAGE plpgsql;
 CREATE FUNCTION eql_v2.meta_data(val eql_v2_encrypted)
   RETURNS jsonb
   IMMUTABLE STRICT PARALLEL SAFE
+  LANGUAGE SQL
 AS $$
-  BEGIN
-     RETURN eql_v2.meta_data(val.data);
-  END;
-$$ LANGUAGE plpgsql;
+    SELECT eql_v2.meta_data(val.data);
+$$;