Apakah pernyataan subquery mysql?-tutorial mysql-php.cn

Pernyataan subquery MySQL merujuk kepada klausa SELECT dalam pernyataan pertanyaan lain, contohnya, "SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);".

Apakah pernyataan subquery mysql?

Persekitaran pengendalian artikel ini: sistem Windows 7, mysql versi 5.7, komputer Dell G3.

Apakah pernyataan subquery mysql?

penyataan subquery mysql:

1. Subquery merujuk kepada klausa SELECT dalam pernyataan pertanyaan lain.

Contoh:

  SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);

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Antaranya, SELECT * FROM t1 ... dipanggil Outer Query (atau Outer Statement),

SELECT column1 FROM t2 Called Sub Query [sub pertanyaan].

Oleh itu, kami katakan bahawa subkueri bersarang di dalam pertanyaan luar. Malah, adalah mungkin untuk menyarangkan subkueri dalam subkueri.

Subkueri mesti muncul di antara kurungan.

Subkueri peringkat baris

  SELECT * FROM t1 WHERE (col1,col2) = (SELECT col3, col4 FROM t2 WHERE id = 10);
  SELECT * FROM t1 WHERE ROW(col1,col2) = (SELECT col3, col4 FROM t2 WHERE id = 10);

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Hasil pulangan subkueri peringkat baris adalah paling banyak satu baris.

Optimumkan subquery

-- Cipta jadual data

CREATE TABLE IF NOT EXISTS tdb_goods(
    goods_id    SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    goods_name  VARCHAR(150) NOT NULL,
    goods_cate  VARCHAR(40)  NOT NULL,
    brand_name  VARCHAR(40)  NOT NULL,
    goods_price DECIMAL(15,3) UNSIGNED NOT NULL DEFAULT 0,
    is_show     BOOLEAN NOT NULL DEFAULT 1,
    is_saleoff  BOOLEAN NOT NULL DEFAULT 0
  );

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-- Tulis rekod

INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;R510VC 15.6英寸笔记本&#39;,&#39;笔记本&#39;,&#39;华硕&#39;,&#39;3399&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;Y400N 14.0英寸笔记本电脑&#39;,&#39;笔记本&#39;,&#39;联想&#39;,&#39;4899&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;G150TH 15.6英寸游戏本&#39;,&#39;游戏本&#39;,&#39;雷神&#39;,&#39;8499&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;X550CC 15.6英寸笔记本&#39;,&#39;笔记本&#39;,&#39;华硕&#39;,&#39;2799&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;X240(20ALA0EYCD) 12.5英寸超极本&#39;,&#39;超级本&#39;,&#39;联想&#39;,&#39;4999&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;U330P 13.3英寸超极本&#39;,&#39;超级本&#39;,&#39;联想&#39;,&#39;4299&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;SVP13226SCB 13.3英寸触控超极本&#39;,&#39;超级本&#39;,&#39;索尼&#39;,&#39;7999&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;iPad mini MD531CH/A 7.9英寸平板电脑&#39;,&#39;平板电脑&#39;,&#39;苹果&#39;,&#39;1998&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;iPad Air MD788CH/A 9.7英寸平板电脑 （16G WiFi版）&#39;,&#39;平板电脑&#39;,&#39;苹果&#39;,&#39;3388&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39; iPad mini ME279CH/A 配备 Retina 显示屏 7.9英寸平板电脑 （16G WiFi版）&#39;,&#39;平板电脑&#39;,&#39;苹果&#39;,&#39;2788&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;IdeaCentre C340 20英寸一体电脑 &#39;,&#39;台式机&#39;,&#39;联想&#39;,&#39;3499&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;Vostro 3800-R1206 台式电脑&#39;,&#39;台式机&#39;,&#39;戴尔&#39;,&#39;2899&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;iMac ME086CH/A 21.5英寸一体电脑&#39;,&#39;台式机&#39;,&#39;苹果&#39;,&#39;9188&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;AT7-7414LP 台式电脑 （i5-3450四核 4G 500G 2G独显 DVD 键鼠 Linux ）&#39;,&#39;台式机&#39;,&#39;宏碁&#39;,&#39;3699&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;Z220SFF F4F06PA工作站&#39;,&#39;服务器/工作站&#39;,&#39;惠普&#39;,&#39;4288&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;PowerEdge T110 II服务器&#39;,&#39;服务器/工作站&#39;,&#39;戴尔&#39;,&#39;5388&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;Mac Pro MD878CH/A 专业级台式电脑&#39;,&#39;服务器/工作站&#39;,&#39;苹果&#39;,&#39;28888&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39; HMZ-T3W 头戴显示设备&#39;,&#39;笔记本配件&#39;,&#39;索尼&#39;,&#39;6999&#39;,DEFAULT,DEFAULT);
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;商务双肩背包&#39;,&#39;笔记本配件&#39;,&#39;索尼&#39;,&#39;99&#39;,DEFAULT,DEFAULT);
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;X3250 M4机架式服务器 2583i14&#39;,&#39;服务器/工作站&#39;,&#39;IBM&#39;,&#39;6888&#39;,DEFAULT,DEFAULT);
 
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;玄龙精英版 笔记本散热器&#39;,&#39;笔记本配件&#39;,&#39;九州风神&#39;,&#39;&#39;,DEFAULT,DEFAULT);
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39; HMZ-T3W 头戴显示设备&#39;,&#39;笔记本配件&#39;,&#39;索尼&#39;,&#39;6999&#39;,DEFAULT,DEFAULT);
 INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(&#39;商务双肩背包&#39;,&#39;笔记本配件&#39;,&#39;索尼&#39;,&#39;99&#39;,DEFAULT,DEFAULT);

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-- Cari semua produk komputer Harga purata, dan kekalkan dua tempat perpuluhan, AVG, MAX, MIN, COUNT, SUM ialah fungsi agregat

SELECT ROUND(AVG(goods_price),2) AS avg_price FROM tdb_goods;

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-- Tanya semua produk yang harganya lebih tinggi daripada harga purata dan isikan mengikut harga dalam tertib menurun

SELECT goods_id,goods_name,goods_price FROM tdb_goods WHERE goods_price > 5845.10 ORDER BY goods_price DESC;

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-- Gunakan subquery untuk melaksanakan

SELECT goods_id,goods_name,goods_price FROM tdb_goods 
  WHERE goods_price > (SELECT ROUND(AVG(goods_price),2) AS avg_price FROM tdb_goods) 
  ORDER BY goods_price DESC;

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-- Soal harga barangan jenis "Super Notebook"

SELECT goods_price FROM tdb_goods WHERE goods_cate = &#39;超级本&#39;;

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-- Produk pertanyaan yang harganya lebih besar daripada atau sama dengan harga "Ultrabook" dan isikannya dalam tertib menurun mengikut harga

SELECT goods_id,goods_name,goods_price FROM tdb_goods 
   WHERE goods_price = ANY(SELECT goods_price FROM tdb_goods WHERE goods_cate = &#39;超级本&#39;)
   ORDER BY goods_price DESC;

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-- = ANY Atau = SESETENGAH yang bersamaan dengan IN

SELECT goods_id,goods_name,goods_price FROM tdb_goods 
   WHERE goods_price IN (SELECT goods_price FROM tdb_goods WHERE goods_cate = &#39;超级本&#39;)
   ORDER BY goods_price DESC;

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--Buat jadual "Klasifikasi Produk"

CREATE TABLE IF NOT EXISTS tdb_goods_cates(
    cate_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    
    cate_name VARCHAR(40)
  );

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--Soal semua rekod jadual tdb_goods dan kumpulkan mengikut "kategori"

  SELECT goods_cate FROM tdb_goods GROUP BY goods_cate;

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-- Tulis hasil pengumpulan ke jadual data tdb_goods_cates

 INSERT tdb_goods_cates (cate_name) SELECT goods_cate FROM tdb_goods GROUP BY goods_cate;

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-- Kemas kini jadual tdb_goods melalui jadual data tdb_goods_cates

UPDATE tdb_goods INNER JOIN tdb_goods_cates ON goods_cate = cate_name 
  SET goods_cate = cate_id ;

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-- Melalui CREATE ...PILIH untuk mencipta jadual data dan menulis rekod pada masa yang sama

-- SELECT brand_name FROM tdb_goods GROUP BY brand_name;
  CREATE TABLE tdb_goods_brands (
    brand_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    brand_name VARCHAR(40) NOT NULL
  ) SELECT brand_name FROM tdb_goods GROUP BY brand_name;

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-- Kemas kini jadual data tdb_goods melalui tdb_goods_brands jadual data (ralat)

UPDATE tdb_goods  INNER JOIN tdb_goods_brands ON brand_name = brand_name
  SET brand_name = brand_id;
  -- Column &#39;brand_name&#39; in field list is ambigous

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-- Betul

  UPDATE tdb_goods AS  g  INNER JOIN tdb_goods_brands AS b ON g.brand_name = b.brand_name
  SET g.brand_name = b.brand_id;

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-- Lihat struktur jadual data tdb_goods

DESC tdb_goods;

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-- Ubah suai jadual data struktur melalui pernyataan ALTER TABLE

ALTER TABLE tdb_goods  
  CHANGE goods_cate cate_id SMALLINT UNSIGNED NOT NULL,
  CHANGE brand_name brand_id SMALLINT UNSIGNED NOT NULL;
  
-- 分别在tdb_goods_cates和tdb_goods_brands表插入记录
   INSERT tdb_goods_cates(cate_name) VALUES(&#39;路由器&#39;),(&#39;交换机&#39;),(&#39;网卡&#39;);
   INSERT tdb_goods_brands(brand_name) VALUES(&#39;海尔&#39;),(&#39;清华同方&#39;),(&#39;神舟&#39;);

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- - Tulis sebarang rekod dalam jadual data tdb_goods

INSERT tdb_goods(goods_name,cate_id,brand_id,goods_price) VALUES(&#39; LaserJet Pro P1606dn 黑白激光打印机&#39;,&#39;12&#39;,&#39;4&#39;,&#39;1849&#39;);

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-- Tanya maklumat terperinci semua produk (dilaksanakan melalui sambungan dalaman)

 SELECT goods_id,goods_name,cate_name,brand_name,goods_price FROM tdb_goods AS g
   INNER JOIN tdb_goods_cates AS c ON g.cate_id = c.cate_id
   INNER JOIN tdb_goods_brands AS b ON g.brand_id = b.brand_id\G;

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-- Tanya maklumat terperinci semua produk ( Dilaksanakan melalui gabungan luar kiri)

   SELECT goods_id,goods_name,cate_name,brand_name,goods_price FROM tdb_goods AS g
   LEFT JOIN tdb_goods_cates AS c ON g.cate_id = c.cate_id
   LEFT JOIN tdb_goods_brands AS b ON g.brand_id = b.brand_id\G;

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-- Tanya maklumat terperinci semua produk (dilaksanakan melalui gabungan luar kanan)

SELECT goods_id,goods_name,cate_name,brand_name,goods_price FROM tdb_goods AS g
   RIGHT JOIN tdb_goods_cates AS c ON g.cate_id = c.cate_id
   RIGHT JOIN tdb_goods_brands AS b ON g.brand_id = b.brand_id\G;

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-- Reka bentuk jadual data klasifikasi tanpa had

CREATE TABLE tdb_goods_types(
     type_id   SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
     type_name VARCHAR(20) NOT NULL,
     parent_id SMALLINT UNSIGNED NOT NULL DEFAULT 0
  ); 
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;家用电器&#39;,DEFAULT);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;电脑、办公&#39;,DEFAULT);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;大家电&#39;,1);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;生活电器&#39;,1);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;平板电视&#39;,3);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;空调&#39;,3);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;电风扇&#39;,4);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;饮水机&#39;,4);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;电脑整机&#39;,2);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;电脑配件&#39;,2);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;笔记本&#39;,9);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;超级本&#39;,9);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;游戏本&#39;,9);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;CPU&#39;,10);
  INSERT tdb_goods_types(type_name,parent_id) VALUES(&#39;主机&#39;,10);

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-- Cari semua kategori dan kategori induknya

  SELECT s.type_id,s.type_name,p.type_name FROM tdb_goods_types AS s LEFT JOIN tdb_goods_types AS  p ON s.parent_id = p.type_id;

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-- Cari semua kategori dan subkategorinya

  SELECT p.type_id,p.type_name,s.type_name FROM tdb_goods_types AS p LEFT JOIN tdb_goods_types AS  s ON s.parent_id = p.type_id;

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-- Cari nombor semua kategori dan subkategorinya

SELECT p.type_id,p.type_name,count(s.type_name) AS children_count FROM tdb_goods_types AS p LEFT JOIN tdb_goods_types AS s ON s.parent_id = p.type_id GROUP BY p.type_name ORDER BY p.type_id;

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-- Tambahkan medan child_count pada tdb_goods_types

ALTER TABLE tdb_goods_types ADD child_count MEDIUMINT UNSIGNED NOT NULL DEFAULT 0;

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-- Kemas kini bilangan subkategori yang baru ditanya ke jadual data tdb_goods_types

UPDATE tdb_goods_types AS t1 INNER JOIN ( SELECT p.type_id,p.type_name,count(s.type_name) AS children_count FROM tdb_goods_types AS p 
                                            LEFT JOIN tdb_goods_types AS s ON s.parent_id = p.type_id 
                             
                                            GROUP BY p.type_name 
                                            ORDER BY p.type_id ) AS t2 
  ON  t1.type_id = t2.type_id 
  SET t1.child_count = t2.children_count;

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-- Salin dua rekod dengan nombor 12 dan 20

SELECT * FROM tdb_goods WHERE goods_id IN (19,20);

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-- INSERT .. . PILIH untuk menyalin

INSERT tdb_goods(goods_name,cate_id,brand_id) SELECT goods_name,cate_id,brand_id FROM tdb_goods WHERE goods_id IN (19,20);

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-- Cari Rekod Pendua

SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING count(goods_name) >= 2;

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--Padamkan rekod pendua

  DELETE t1 FROM tdb_goods AS t1 LEFT JOIN (SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING count(goods_name) >= 2 ) AS t2  ON t1.goods_name = t2.goods_name  WHERE t1.goods_id > t2.goods_id;

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