how to optimize sql query with multiple joins

The original author seems to be called TopCat, I have understood a bit by the memory to write down the standby.If you use the Select Name from Studenttable, the results displayed are:NameTomJohn doeIf you use the Select Row_number () as Rowindex,name from studenttable, the result isROWINDEX Name1 sheets of three2 DickOf course, the result of a generic query is that there is no need to add numbers, because the list itself is numbered when the data is d

: SELECT * from Order WHERE customer_id=1 and subtotal>100 $orders=$customer->getorders ()->where (' subtotal>100 ')All (); Copy Code query 100 customer, each customer's total is greater than 100 of the order//The following code executes the SQL statement://select * FROM Customer LIMIT +//select * from Order WHERE customer_id in (,...) and subtotal>100 $customers= Customer::find ()->limit (+)With ([' Orders

When you execute an SQL query and UPDATE multiple rows of records, we usually use the following SQL statement to UPDATE the field value: 1 UPDATE mytable SET myfield = 'value' WHERE other_field = 'other _ value'; however, if you want to UPDATE multiple rows of data and each

Execute an SQL query and UPDATE multiple rows to record bitsCN.com Execute an SQL query and UPDATE multiple rows of records Generally, the following SQL statement is used to update th

sets. Oracle stores this activity set in the named cursor of the display definition that you create. Oracle cursors are a mechanism for easy processing of multiple rows of data, and without cursors, Oracle developers must individually and explicitly retrieve and manage each record selected by the cursor query. Another function of the cursor that contains a pointer to the record that is currently being acce

Spelling skills of SQL statements with multiple query conditions. Spelling skills of SQL statements with multiple query conditions. $ SQL = "select nbsp; * nbsp; from nbsp; tb1"; if

Spelling skills of SQL statements with multiple query conditions. Spelling skills of SQL statements with multiple query conditions. $ Sqlselect nbsp; * nbsp; from nbsp; tb1; if ($ id]) {$ where. nbsp; where nbsp; id nbsp; li

In our project development, we often encounter the requirements of multiple conditional fuzzy queries. There are two common solutions for this: one is to stitch the SQL string at the end of the program, construct the corresponding SQL string based on whether a condition is selected, and use the dynamic SQL statement in

Spelling skills of SQL statements with multiple query conditions. Spelling skills of SQL statements with multiple query conditions. $ Sqlselect nbsp; * nbsp; from nbsp; tb1; if ($ id]) {$ where. nbsp; where nbsp; id nbsp; li

1. What is the cursor? Oracle uses two types of cursor: explicit cursor and implicit cursor. No matter how many records are returned by the statement, PL/SQL implicitly declares a cursor for each SQL command, such as UPDATE, DELETE, and INSERT. To manage SQL statement processing, you must implicitly define a cursor for it .) The user declares and uses the displa

Tags: span work SQL statement report has a one-to-many advantage blog isFirst, let's look at a demand.You have a table user table A and a user detail table B and a sales order form C A---->b one-to-many relationship a---->c one-to-many relationship If you select a Join B on (foreign key of B and A) query out 2 result sets If you select a Join C on (foreign key of C and a)

SQL server allows you to quickly query information about a table among multiple databases. This example describes how SQL server can quickly query information of a table among multiple databases. We will share this with you for yo

If the structures of multiple tables are different, it seems impossible to query the results of multiple tables together! For example, Table If the structures of multiple tables are different, it seems impossible to query the results of