sql: change rules used to determine NULLIF() type

This patch introduces new rules to determine type of NULLIF() built-in
function.

Closes tarantool#6990

@TarantoolBot document
Title: New rules to determine type of result of NULLIF

The type of the result of NULLIF() function now matches the type of the
first argument.

changelogs/unreleased/gh-6989-type-of-NULLIF.md

@@ -0,0 +1,4 @@
+## feature/sql
+
+* Now the type of result of NULLIF() is the same as the type of the first
+ argument (gh-6989).

src/box/sql/func.c

@@ -355,6 +355,12 @@ func_nullif(struct sql_context *ctx, int argc, const struct Mem *argv)
 {
  assert(argc == 2);
  (void)argc;
+ if (!mem_is_comparable(&argv[1])) {
+ ctx->is_aborted = true;
+ diag_set(ClientError, ER_SQL_TYPE_MISMATCH, mem_str(&argv[1]),
+ "scalar");
+ return;
+ }
  if (mem_cmp_scalar(&argv[0], &argv[1], ctx->coll) == 0)
  return;
  if (mem_copy(ctx->pOut, &argv[0]) != 0)
@@ -1954,8 +1960,27 @@ static struct sql_func_definition definitions[] = {
  {"MIN", 1, {FIELD_TYPE_SCALAR}, FIELD_TYPE_SCALAR, step_minmax, NULL},
  {"NOW", 0, {}, FIELD_TYPE_DATETIME, func_now, NULL},
 
- {"NULLIF", 2, {FIELD_TYPE_SCALAR, FIELD_TYPE_SCALAR}, FIELD_TYPE_SCALAR,
+ {"NULLIF", 2, {FIELD_TYPE_SCALAR, field_type_MAX}, FIELD_TYPE_SCALAR,
+ func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_UNSIGNED, field_type_MAX},
+ FIELD_TYPE_UNSIGNED, func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_STRING, field_type_MAX}, FIELD_TYPE_STRING,
  func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_DOUBLE, field_type_MAX}, FIELD_TYPE_DOUBLE,
+ func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_INTEGER, field_type_MAX},
+ FIELD_TYPE_INTEGER, func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_BOOLEAN, field_type_MAX},
+ FIELD_TYPE_BOOLEAN, func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_VARBINARY, field_type_MAX},
+ FIELD_TYPE_VARBINARY, func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_DECIMAL, field_type_MAX},
+ FIELD_TYPE_DECIMAL, func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_UUID, field_type_MAX}, FIELD_TYPE_UUID,
+ func_nullif, NULL},
+ {"NULLIF", 2, {FIELD_TYPE_DATETIME, field_type_MAX},
+ FIELD_TYPE_DATETIME, func_nullif, NULL},
+
  {"POSITION", 2, {FIELD_TYPE_STRING, FIELD_TYPE_STRING},
  FIELD_TYPE_INTEGER, func_position_characters, NULL},
  {"POSITION", 2, {FIELD_TYPE_VARBINARY, FIELD_TYPE_VARBINARY},

test/sql-luatest/gh_6989_nullif_result_type_test.lua

@@ -0,0 +1,36 @@
+local server = require('test.luatest_helpers.server')
+local t = require('luatest')
+local g = t.group()
+
+g.before_all(function()
+ g.server = server:new({alias = 'test_assertion_in_modulo'})
+ g.server:start()
+end)
+
+g.after_all(function()
+ g.server:stop()
+end)
+
+g.test_assertion_in_modulo = function()
+ g.server:exec(function()
+ local t = require('luatest')
+ local sql = "SELECT nullif(1, '2');"
+ local res = "integer"
+ t.assert_equals(box.execute(sql).metadata[1].type, res)
+
+ sql = "SELECT nullif('1', '1');"
+ res = "string"
+ t.assert_equals(box.execute(sql).metadata[1].type, res)
+
+ sql = "SELECT nullif([1], '2');"
+ res = "Failed to execute SQL statement: wrong arguments for function "..
+ "NULLIF()"
+ local _, err = box.execute(sql)
+ t.assert_equals(err.message, res)
+
+ sql = "SELECT nullif(1, [2]);"
+ res = "Type mismatch: can not convert array([2]) to scalar"
+ _, err = box.execute(sql)
+ t.assert_equals(err.message, res)
+ end)
+end

test/sql-tap/array.test.lua

@@ -827,8 +827,7 @@ test:do_catchsql_test(
  [[
  SELECT NULLIF(1, a) FROM t;
  ]], {
- 1,
- "Failed to execute SQL statement: wrong arguments for function NULLIF()"
+ 1, "Type mismatch: can not convert array([123]) to scalar"
  })
 
 test:do_catchsql_test(

test/sql-tap/map.test.lua

@@ -830,8 +830,7 @@ test:do_catchsql_test(
  [[
  SELECT NULLIF(1, m) FROM t;
  ]], {
- 1,
- "Failed to execute SQL statement: wrong arguments for function NULLIF()"
+ 1, [[Type mismatch: can not convert map({"abc": 123}) to scalar]]
  })
 
 test:do_catchsql_test(