Akina

CREATE TABLE log AS (
  WITH cte AS (
    SELECT STRING_TO_ARRAY(txt, ' ') parsed
    FROM t1
  )
  SELECT LEFT(parsed[2], 8) :: DATE dt,
         parsed[3] link,
         ARRAY_TO_STRING(parsed[6:100], ' ') agent,
         t2.city
  FROM cte
  LEFT JOIN t2 ON cte.parsed[1] = t2.ip
  );

SELECT *
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE TABLE_SCHEMA = DATABASE() /* либо 'database_name' */
  AND TABLE_NAME = 'table_name'

SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
  AND TABLE_NAME = 'table_name'

Select * 
from Employees
where [Employee ID] != ALL ( SELECT 90 UNION SELECT NULL );

SELECT categories.id, 
       categories.slug,  
       ct_ru.title title_ru,  
       ct_en.title title_en,  
       ct_de.title title_de
FROM categories
LEFT JOIN category_translations ct_ru ON category_translations.category_id=categories.id 
                                     AND category_translations.locale = 'ru'
LEFT JOIN category_translations ct_en ON category_translations.category_id=categories.id 
                                     AND category_translations.locale = 'en'
LEFT JOIN category_translations ct_de ON category_translations.category_id=categories.id 
                                     AND category_translations.locale = 'de';

WITH cte AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY score DESC) rn
    FROM source_table
)
SELECT *
FROM cte
WHERE rn = 1
-- ORDER BY score DESC LIMIT nnn
;

CREATE TRIGGER trigger_name
EVENT ACTION ON table_name
FOR EACH ROW
BEGIN
    SET @trigger_name_table_name = CONCAT('executed, ', 'column_value=', NEW.column);
-- trigger action
    SET @trigger_name_table_name = NULL;
END;

будет ли использоваться индекс в запросе вида WHERE `field1` LIKE '_aa_a_'?