Константин Цветков

SELECT CYear AS Date,
  (SELECT COUNT(*) FROM COMPANIES WHERE (YEAR(reg_date) = CY.CYear)) AS opened_count,
  (SELECT COUNT(*) FROM COMPANIES WHERE (YEAR(terminate_date) = CY.CYear)) AS terminate_count
  FROM (
    SELECT YEAR(C1.reg_date) AS CYear
      FROM COMPANIES AS C1
      WHERE (NOT (C1.reg_date IS NULL))
    UNION
    SELECT YEAR(C2.terminate_date) AS CYear
      FROM COMPANIES AS C2
      WHERE (NOT (C2.terminate_date IS NULL))) AS CY

SELECT LEFT( Text, LOCATE( 'поиска', Text ) + LENGTH ('поиска') - 1)
  FROM Texts
  WHERE Text LIKE '%поиска%'

Вам нужно добавить:GROUP BY events.id
Например
Всё работает:

CREATE TABLE `author` (
   `id` INT(10) NOT NULL,
   `name` VARCHAR(200) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
   `fam` VARCHAR(200) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
   `birthday` DATE NULL DEFAULT NULL,
   PRIMARY KEY (`id`)
);
 
CREATE TABLE `books` (
   `id` INT(10),
   `id_author` INT(10) NULL DEFAULT NULL,
   `book` VARCHAR(500) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
   PRIMARY KEY (`id`),
   INDEX `id_author` (`id_author`)
);

INSERT INTO `author` (`id`, `name`, `fam`, `birthday`) VALUES (1, 'Николай Николаевич', 'Носов', '2008-11-23');
INSERT INTO `author` (`id`, `name`, `fam`, `birthday`) VALUES (2, 'Артур Конан', 'Дойль', '1859-05-22');
 
INSERT INTO `books` (`id`, `id_author`, `book`) VALUES (1, 1, 'Незнайка учится');
INSERT INTO `books` (`id`, `id_author`, `book`) VALUES (2, 1, 'Незнайка-путешественник');
INSERT INTO `books` (`id`, `id_author`, `book`) VALUES (3, 1, 'Винтик, Шпунтик и пылесос');

SELECT a.id, a.name, a.fam, GROUP_CONCAT(DISTINCT b.book ORDER BY b.book ASC SEPARATOR ', ') AS books
FROM `author` a
LEFT JOIN `books` b ON a.id=b.id_author
GROUP BY a.id;

Выбрать КодПокупателя из ПокупательПродукт 
  где КодПродукта равен ДанныйТовар 
  групировать по КодПокупателя 
  HAVING количество меньше 2

SELECT a1.object_id 
  FROM activity AS a1
    LEFT JOIN activity AS a2 ON a2.object_id = a1.object_id 
  WHERE a1.subject = "added" AND a2.subject = "remove" AND a2.object_id IS NULL

Группируйте по

CASE WHEN User_ID1 > User_ID2 THEN CONCAT ( User_ID2, '-', User_ID1 )
  ELSE CONCAT ( User_ID1, '-', User_ID2 )
END CASE

SELECT Concat(calendar.name, " ", calendar.year) as name, ifnull(date.value1,0) AS value
 FROM (SELECT DISTINCT date.year, month.id, month.name FROM date, month) AS calendar
   LEFT JOIN date
     ON date.year = calendar.year AND date.month_id = calendar.id
 ORDER BY calendar.year, calendar.id LIMIT 6 OFFSET 18

ограничиваясь текущим месяцем … последние 6

SELECT Concat(calendar.name, " ", calendar.year) as name, ifnull(date.value1,0) AS value
 FROM (SELECT DISTINCT date.year, month.id, month.name FROM date, month) AS calendar
   LEFT JOIN date
     ON date.year = calendar.year AND date.month_id = calendar.id
  WHERE CONCAT(calendar.year, '-', LPAD( calendar.id, 2, '0')) 
                 > LEFT(DATE_SUB(NOW(), INTERVAL 6 MONTH), 7)
 ORDER BY calendar.year, calendar.id LIMIT 6

SELECT DISTINCT tag_id FROM news_tag WHERE theme_id = КодСтрогоЗаданнойТемы

потому что он есть в обеих статьях

SELECT tag_id
  FROM news_tag
  WHERE (theme_id = 1)
  GROUP BY tag_id
  HAVING COUNT(news_id) = ( SELECT COUNT(DISTINCT(news_id)) FROM news_tag WHERE (theme_id = 1) )

SELECT MAX(start_diameter) FROM table_name WHERE (start_diameter <= 145)
UNION ALL
SELECT MIN(start_diameter) FROM table_name WHERE (start_diameter >= 145)

Группировка по указанным полям и максимальная дата. Если вам нужен ещё и код, то свяжите результат с основной таблицей по указанным полям и дате.