1.1 常见连接类型 INNER JOIN(内连接):返回两个表中满足条件的交集。 LEFT JOIN(左外连接):返回左表的所有记录以及右表中匹配的记录。 RIGHT JOIN(右外连接):返回右表的所有记录以及左表中匹配的记录。 FULL JOIN(全外连接):返回两个表中所有记录,未匹配的部分用NULL填充。 CROSS JOIN(交叉连接):返回两个表...
2) Using PostgreSQL NATURAL JOIN to perform a LEFT JOIN The following example uses the NATURAL JOIN clause to perform a LEFT JOIN without specifying the matching column: SELECT * FROM categories NATURAL LEFT JOIN products; Output: category_id | category_name | product_id | product_name ---+...
tip 6 对于数组可以用unnest函数化为多行然后left join,例如select * from pg_index对于系统的索引表中 indkey字段,对于复合主键就需要化为多行然后关联 unnest(anyarray)setof anyelementexpand an array to a set of rowsunnest(ARRAY[1,2]) 1 2 (2 rows) tip7 sql中添加表的时候对于以下敏感字可以加上...
CREATE INDEX c_idx2 ON locktest(c);ALTER TABLE locktest ADD COLUMN c2 INT;CREATE INDEX c2_idx ON locktest(c2);-- unfinished example transaction BEGIN;UPDATE locktest SETc=3WHEREc=1;-- second connectionpostgres=# SELECT * FROM lockview;pid|vxid|lock_type|lock_mode|granted|xid_lock|rel...
但是,我想考虑一种情况,即某个键没有名为attr_name1的属性,并在新表的相应列中插入空值。我不知道如何实现这一目标。我对使用多个查询或中间表等没有问题,但是表中有相当多的行,我需要可以扩展到数百万行的东西。 任何帮助都将不胜感激。 Example:
For example: SELECT a, fruit_a, b, fruit_b FROM basket_a LEFT JOIN basket_b ON fruit_a = fruit_b WHERE b IS NULL; The output is: a | fruit_a | b | fruit_b ---+---+---+--- 3 | Banana | null | null 4 | Cucumber | null | null (2 rows) Note that the LEFT JOIN...
By using FULL JOIN we will get all records from both the categories table and the testproducts table:Example Join testproducts to categories using the category_id column: SELECT testproduct_id, product_name, category_name FROM testproducts FULL JOIN categories ON testproducts.category_id = ...
In this example, this table holds the information of the table ‘tbl_a’ such as the oid of this table and the name of this table. The join tree stores the FROM clause and the WHERE clauses. The sort clause is a list of SortGroupClause. 3 查询重写 展开子查询的视图、一些常量函数等...
(polroles) ORDER BY 1 ), E', ') ELSE E'' END FROM pg_catalog.pg_policy pol WHERE polrelid = c.oid), E'\n') AS "Policies" FROM pg_catalog.pg_class c LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace WHERE c.relkind IN ('r', 'v', 'm', 'S', 'f'...
Fixed an issue with handling of column name alias which may cause client to hang if column name alias contains string of length more than 64 bytes, for example, select col as '您对“数据一览“中的车型,颜色,内饰,选装, '. Fixed datatype of information_schema_tsql.tables.TABLE_TYPE column....