Akina

SELECT TOP 500 * 
FROM [table] 
WHERE  NOT EXISTS ( SELECT NULL 
                    FROM [Entities] 
                    WHERE [column] = '2' 
                      AND [table1].[Id] = [ClientTableId] )

создать миллион пустых строк

WITH RECURSIVE 
cte AS ( SELECT 1 n
         UNION ALL
         SELECT n + 1  FROM cte WHERE n < 1000 )
INSERT INTO tablename (id)
SELECT NULL FROM cte t1 CROSS JOIN cte t2;

SELECT DISTINCT user_id
FROM enter t1
WHERE NOT EXISTS ( SELECT NULL
                   FROM enter t2
                   WHERE enter_source = 'web' 
                     AND t1.user_id = t2.user_id )
  AND EXISTS ( SELECT NULL
               FROM enter t3
               WHERE enter_source IN ('ios', 'android')
                 AND t1.user_id = t3.user_id );

DROP PROCEDURE IF EXISTS get_artist;
DELIMITER ;;
CREATE PROCEDURE get_artist(IN artist_id integer(11), IN show_links integer(1))
BEGIN
    CASE WHEN show_links=1
         THEN 
             SELECT * 
             FROM artist 
             where id = artist_id;
         ELSE  
             SELECT * 
             FROM artist 
             LEFT JOIN artist_social_links ON artist_social_links.artist_id = artist_id 
             where id = artist_id ;
    END CASE;
END;;
DELIMITER ;
CALL get_artist(196796, 1);

CREATE TABLE test (entity INT,    -- некая строка в структуре
                   position INT); -- её позиция при сортировке

UPDATE test
SET position := CASE WHEN position = @from 
                     THEN @to
                     ELSE position + SIGN(@from - @to)
                     END
WHERE position BETWEEN LEAST(@from, @to) AND GREATEST(@from, @to);

SELECT priority,
       SUM(time >= '2021-06-04' AND time < '2021-06-05') AS today,
       SUM(time >= '2021-06-03' AND time < '2021-06-04') AS yesterday
FROM  tableX
WHERE time >= '2021-06-03' AND time <= '2021-06-05'
GROUP BY priority

CREATE TABLE schedule ( schedule_id INT PRIMARY KEY,
                        start_time TIME,
                        task_id INT );

что если я запущу программу, а нужной таблицы не будет?

дошёл до такой функции

SELECT TABLE_SCHEMA, TABLE_NAME
FROM INFORMATION_SCHEMA.TABLES
-- WHERE TABLE_NAME = 'my_table_name'
;

что если в другой схеме уже есть таблица с таким названием...

SELECT a.login
FROM account a
JOIN transactions t ON a.id = t.account_id
JOIN game g ON t.game_id = g.id
JOIN company c ON c.id = g.Developer
GROUP BY a.login
HAVING !SUM( c.country != 'USA' OR YEAR(g.Release_date) MOD 2 )