Evaluate SQL expressions for zero

Which of the following SQL expressions evaluate to 0? Evaluate each independently, justify the result, and note any dialect-specific behavior (e.g., MySQL type coercion rules):

1. SELECT '0' = 0;
2. SELECT 0 IS FALSE;
3. SELECT '0' IS FALSE;
4. SELECT STRCMP('0', 0). State your assumptions about the SQL dialect.

Evaluate MySQL expressions for zero

Assume PostgreSQL as the SQL dialect. This question probes how PostgreSQL applies type coercion and boolean evaluation. Consider the following four expressions, each evaluated independently:

1. '0' = 0 — comparing the string literal '0' to the integer 0 (PostgreSQL coerces the untyped string literal to integer).
2. (0)::boolean IS FALSE — casting the integer 0 to boolean, then testing IS FALSE.
3. '0'::boolean IS FALSE — casting the string '0' to boolean, then testing IS FALSE.
4. The sign of comparing the string '0' to the string '0' (a STRCMP-style comparison): -1 if the left side sorts before the right, 1 if after, and 0 if they are equal.

Write a single SQL query (no input tables are needed — build the rows with literals) that evaluates all four expressions and returns exactly one row per expression with these columns:

• expr_id — an integer from 1 to 4 identifying the expression.
• expression_text — a short text label describing the expression.
• result_value — the integer result of the expression: cast boolean results to integer (TRUE → 1, FALSE → 0); for the comparison in expression 4 return its sign as -1, 0, or 1.

Order the output by expr_id ascending. The output should make clear which expression evaluates to 0: only the string-comparison sign in expression 4 is 0 (the two strings are equal); the other three all evaluate to 1.

Expected output

Four rows (one per expression) giving each expression's integer result; only the string-comparison sign (expr 4) is 0, the rest are 1.

expr_id	expression_text	result_value
1	'0' = 0 (string-to-int coercion)	1
2	(0)::boolean IS FALSE	1
3	'0'::boolean IS FALSE	1
4	SIGN of comparing '0' to '0'	0

Hints

1. No tables are required — assemble the four result rows with literal SELECTs joined by UNION ALL.
2. Cast boolean results to integer with ::int so TRUE becomes 1 and FALSE becomes 0; in PostgreSQL the string '0' is a valid boolean literal for FALSE.
3. Reproduce a STRCMP-style comparison with a CASE expression that returns -1, 1, or 0 based on < / > / equality of the two strings.