join table postgres

-------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 3328K| 158M| 640 (5)| 00:00:08 | |* 1 | HASH JOIN | | 3328K| 158M| 640 (5)| 00:00:08 | | 2 | VIEW | TB_VIEW | 3306 | 42978 | 309 (1)| 00:00:04 | | 3 | UNION-ALL | | | | | | |* 4 |

field must appear in the GROUP BY clause when there is an aggregate function and a field that does not use an aggregate function in a query! 2, GROUP By field 1, Field 2, a result set is first grouped by field 1, and then grouped by field 2!3、whereoccurs before GROUP by! 4、whereThere is no aggregation function behind it! Multi-table query: Table Connection classification: Inner connection, outer connection

The join condition can be specified in the From or WHERE clause, and it is recommended that the join condition be specified in the FROM clause. The WHERE and having clauses can also contain search criteria to further filter the rows selected by the join condition.Connections can be divided into the following categories:internal connections. (typical

Tags: type sort BSP Query mode processing power another Ken lexical1. OverviewHash join is a database processing algorithm for multi-table connection, there are two more common ways for multi-table connection: Sort merge-join and nested loop. To give a clearer introduction to the usage scenarios for hash joins and to i

Join Table query There are two ways to query joined tables, ① Internal Association, ② External Association To join a Table query, the first condition is that the two tables must have a field attribute, which is the same as the value, it is to combine the data related to two tables into one

You can retrieve data from two or more tables based on the logical relationship between tables. Connection query is an important feature of relational databases. It is also a major indicator that distinguishes it from other types of database management systems. The syntax format of the join uses the from clause to join from first_table join_type second_table [ON (join_condition)] Join_type: the type of

(); For 100 customers, orders with a sum greater than 100 per customer The following code executes the SQL statement: //select * FROM Customer LIMIT //select * To order WHERE customer_id in (1,2,...) and subtotal>100 $customers = Customer::find ()->limit ()->with ([ ' orders ' => function ($query) { $query->andwhere (' subtotal>100 '); }, ])->all (); Here, the parameter of width is an array, the key is the associated name, and the value is the callback function. That is to s

to avoid errors due to table name and keyword conflicts. Note: If the table method is not defined, the data table corresponding to or defined in the current model is automatically obtained by default. 2. Join method: query Join is supported.

::find ()->limit ()->with ([' orders ' = = function ($query) {$query- >andwhere (' subtotal>100 ');},])->all (); Here the width parameter is an array, the key is the associated name, and the value is the callback function. That is, the activequery of orders, which is returned by this association, executes once $query->andwhere (' subtotal>100 '); Using Joinwith for Table Association We all know that you can use j