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맨 오른쪽의 "category"필드에 표시된대로 각 카테고리에서 6 개 항목을 선택하는 mysql 명령을 작성하려고합니다. 기본적으로 범주의 각 값에 대해 6 개의 레코드가 선택되기를 원합니다. Heres는MySQL : 필드의 모든 고유 값에 대해 고정 된 양의 레코드 선택
내가 사용 오전 SELECT *, 데이타베이스
+--------------------------------------+------------------------------------+--------------+--------+--------------+---------------------------+
| imageLocation | productName | manufacturer | price | availability | category |
+--------------------------------------+------------------------------------+--------------+--------+--------------+---------------------------+
| ./images/Strawberry_Pi_3_Model_B.jpg | Camera Module XF181 | Toro | 35.99 | 10 | Strawberry Pi |
| ./images/Strawberry_Pi_3_Model_B.jpg | Strawberry Pi Extension Kit SG218 | Apollo | 22.99 | 4 | Popular Items |
| ./images/Strawberry_Pi_Zero.jpg | Strawberry Pi Extension Kit AU252 | Gorella | 194.99 | 1 | Strawberry Pi Accessories |
| ./images/Strawberry_Pi_2_Model_B.jpg | Strawberry Pi Case ZM942 | Corona | 182.99 | 7 | Popular Items |
| ./images/Strawberry_Pi_2_Model_B.jpg | Compute Module Kit GP664 | Corona | 16.99 | 1 | Strawberry Pi Accessories |
| ./images/Strawberry_Pi_3_Model_B.jpg | Camera Module CL638 | Apollo | 256.99 | 7 | Strawberry Pi Accessories |
에 명령이이 명령의 처음 몇 줄의 예. 나는 잠시 루프 (가)마다 모든 카테고리에서 루프를 6 개 항목을 선택하여 (이 경우 3) 종류가 있기 때문에이 여러 번 출마 때까지 계속
SET x = 0; WHILE (x < COUNT(SELECT UNIQUE category FROM PRODUCTS) DO SELECT * FROM Products WHERE category IN (SELECT UNIQUE category FROM Products LIMIT x-1,1) LIMIT 6; SET x = x + 1; END WHILE;
내가 오류를 얻고을 실행 사용하고 있습니다
ERROR 1193 (HY000): Unknown system variable 'x'
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHILE (x < COUNT(SELECT UNIQUE category FROM PRODUCTS) DO SELECT * FROM Product' at line 1
ERROR 1193 (HY000): Unknown system variable 'x'
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'END WHILE' at line 1
싶습니다 출력의 예
+--------------------------------------+------------------------------------+--------------+--------+--------------+---------------+
| imageLocation | productName | manufacturer | price | availability | category |
+--------------------------------------+------------------------------------+--------------+--------+--------------+---------------+
| ./images/Strawberry_Pi_3_Model_B.jpg | Camera Module XF181 | Toro | 35.99 | 10 | Strawberry Pi |
| ./images/Camera_Module_V2.jpg | Compute Module Kit GX416 | Belrubi | 98.99 | 1 | Strawberry Pi |
| ./images/Sense_Hat.jpg | Strawberry Pi Extension Kit JJ556 | Toro | 92.99 | 1 | Strawberry Pi |
| ./images/Strawberry_Pi_Zero.jpg | Camera Module FI378 | Belrubi | 44.99 | 5 | Strawberry Pi |
| ./images/Compute_Module.jpg | Compute Module Kit HP564 | Elsanta | 239.99 | 5 | Strawberry Pi |
| ./images/Strawberry_Pi_1_Model_A.jpg | Compute Module UZ736 | Revada | 24.99 | 10 | Strawberry Pi |
| ./images/Strawberry_Pi_3_Model_B.jpg | Strawberry Pi Extension Kit SG218 | Apollo | 22.99 | 4 | Popular Items |
| ./images/Strawberry_Pi_2_Model_B.jpg | Strawberry Pi Case ZM942 | Corona | 182.99 | 7 | Popular Items |
| ./images/placeholder.png | Compute Module VO511 | Darstar | 188.99 | 3 | Popular Items |
| ./images/Strawberry_Pi_2_Model_B.jpg | Strawberry Pi DB112 | Tufts | 79.99 | 1 | Popular Items |
| ./images/Compute_Model_Kit.jpg | Compute Module DX828 | Aliso | 83.99 | 3 | Popular Items |
| ./images/Strawberry_Pi_Zero.jpg | Camera Module SZ841 | Glasso | 115.99 | 6 | Popular Items |
| ./images/Strawberry_Pi_Zero.jpg | Strawberry Pi Extension Kit AU252 | Gorella | 194.99 | 1 | Strawberry Pi Accessories |
| ./images/Strawberry_Pi_2_Model_B.jpg | Compute Module Kit GP664 | Corona | 16.99 | 1 | Strawberry Pi Accessories |
| ./images/Strawberry_Pi_3_Model_B.jpg | Camera Module CL638 | Apollo | 256.99 | 7 | Strawberry Pi Accessories |
| ./images/Strawberry_Pi_Case.jpg | Strawberry Pi LG178 | Tufts | 26.99 | 10 | Strawberry Pi Accessories |
| ./images/Sense_Hat.jpg | Strawberry Pi OW299 | Darstar | 35.99 | 4 | Strawberry Pi Accessories |
| ./images/Compute_Module.jpg | Compute Module Kit QR216 | Confitura | 41.99 | 6 | Strawberry Pi Accessories |
+--------------------------------------+------------------------------------+--------------+--------+--------------+---------------------------+