Summarize the usage of sql statement skills and examples

This article focuses on sorting out the tips for executing sql. This method not only brings convenience in operation, but also ensures the security of data. 1: Query data (guarantee query performance) First, I would like to explain the performance of SELECT * and SELECT t.id, t.name. Conclusion: The performance of the latter is actually better than the former in general. If you don’t believe it, you can test it yourself. When querying, it is best to give the table an alias to facilitate finding the fields to be queried in the table. When executing sql for multi-condition query, use tools such as Navicat to write query sql in the following format: SELECT cus.uuid , cus.customerId FROM `customer` cus where 1=1 and cus.uuid='' --&nb

1. Tips on mysql operation sql

Introduction: This article focuses on organizing tips for executing sql. This method not only brings operational convenience, but also ensures data security.

2. SQL statement skills: cleverly use OR to achieve logical judgment when querying

##Introduction: DECLARE @fieldname varchar(50) DECLARE @fieldvalue nvarchar(100) SET @fieldname='chassisno' --One or none of chassisno, plateno, owner, contacttelno can be passed here Pass SET @fieldvalue='Zuowenjun' IF @fieldname = 'chassisno'

3. MySQL (C API) VC example and code download (1) (2)_PHP tutorial

Introduction: MySQL (C API) VC instance and code download (1) (2). 10. SQL statement skills 1. A SQL statement problem: row and column conversion select * from v_temp The above view results are as follows: user_name role_name ----------------------- -- System Administrator Administrator

4. MySQL (C API) VC instance and code download (1) (2)

Introduction: MySQL (C API) VC instance and code download (1) (2). 10. SQL statement skills 1. A SQL statement problem: row and column conversion select * from v_temp The above view results are as follows: user_name role_name ----------------------- -- System Administrator Administrator

5. SQL statement skills: monthly statistical data

Introduction: SQL Statement skills: Statistics by month

6. SQL statement skills to remove duplicate rows

Introduction: Remove tables If you want to remove duplicate rows of data in a table, you may immediately think of using the DISINTCT keyword, but DISINTCT can only remove rows with the same columns in the table. If you encounter rows that need to remove multiple duplicate fields in the table (ie: part of Same, partially different), so what should we do? Through many years of database writing experience, I have compiled the following methods for your reference

7. SQL statement skills: Query data records that exist in one table but not in another table

Introduction: Method 1 (only applicable to a single field) Use not in, easy to understand, low efficiency select A.ID from A where A.ID not in (select ID from B ) Method 2 (applicable to multiple field matching) Use left join...on..., "B.ID isnull" means select A.ID from A left jo## after the left join in the record where the B.ID field is null. #

The above is the detailed content of Summarize the usage of sql statement skills and examples. For more information, please follow other related articles on the PHP Chinese website!