SQL query statement "3": Multi-Table query (also called connection query, which is a connection query based on two tables)If a query needs to operate on multiple tables, it is called a connection
1. Query all tables in sql:
Select table_name from database name. Information_schema. Tables Where table_type= ' BASE table ' is executed, you can see the names of all the tables in the database that belong to you
2. Query all tables and columns in sql:Select Dbo.sysobjects.name as TABLE_NAME, dbo.syscolumns.name as column_name from Dbo.syscolumns INNER JOIN
Connection Query
You can use the join operator to query multiple tables. Connection is the main feature of the relational database model and a symbol that distinguishes it from other types of database management systems.
In the relational database management system, the relationship between data does not have to be determined when a table is created, and all information about an object is often stored in a
1. query all tables in SQL:Select TABLE_NAME FROM database name. INFORMATION_SCHEMA.TABLES Where TABLE_TYPE = 'base table' after execution, you can see the names of all tables created by yourself in the database.2. query all tables and columns in SQL:Select dbo. sysobjects. name as Table_name, dbo. syscolumns. name AS Column_name FROM dbo. syscolumns inner join dbo. sysobjects ON dbo. syscolumns. id = dbo.
Label:Next: T-SQL Dynamic Query (3)--Static SQLObjective: There's a lot of talk about dynamic queries, and this article describes some of the ways to use dynamic SQL to solve dynamic queries.Why use Dynamic sql: in many projects, dynamic SQL is widely used and even misused,
Grade> = 90
-- Use "logical expression" as the query condition ......
/*
Logical expressions in SQL:
Not: non
And: corresponds
Or: or
*/
Select * from Student
-- Query the student table for a 19-year-old male student.
Select * from Student where Sage = 19 and Ssex = 'male'
-- Query the student whose age is 19 or 20 in
Advanced query technology is mainly related to multiple tables linked query technology, embedded SELECT statement subquery technology, the combination of multiple queries combined technology.
1. Connection Query
You need to retrieve data from two or more tables at the same time. A link allows you to retrieve data from two tables or more than two tables at the s
Tags: SQL statement electronic win style SPAN different statement column DTS --Connect remote SQL or insert data with OPENROWSET
--if only temporary access, you can directly use OPENROWSET
--Query Example
Select * from OpenRowset('SQLOLEDB'
,'SQL Server name';'User name';'Password', database name. dbo. Table name)
Routine collection of commonly used SQL query statements and SQL statements
Common SQL query statements are as follows:
1. Simple query statements
1. view the table structure
SQL> DESC
Label:IntroductionSee a popular blog today. NET Senior Engineer face questions of SQL, asked to find the highest score of each department, and by the department number, the student number in ascending order. This query is more complex, but also more typical, since the use of ORM, a long time did not write SQL statements, so I studied the next, I also wrote a: w
SQL, Structured query Language Structured Query Language , is a database query and programming language for accessing data and querying, updating, and managing relational database systems. SQL language contains 4 sections:※ data definition language (DDL) create ,
), variable length, can hold photos, files, etc.
int, integer field. Example: Userage int
float, floating-point data is approximate. Example: Userresults float, the approximate numeric data type used to represent floating-point numeric data.
datetime, Date type. Example: Createdatetime datetime
Bit, Boolean type. Can be set to True is male, false is schoolgirl
If the content is very much, indeterminate length (such as article), can be used: nvarchar (max) 6. Save the tabl
Steps for Oracle to execute SQL query statements and oraclesql query statements
Steps for Oracle to execute SQL query statements
If you enter the following query statement in SQL * Plus
Optimization of SQL massive data query and non-use like processing solutions, data query like
1. To optimize the query, try to avoid full table scanning. First, consider creating an index on the columns involved in where and order.
2. Try to avoid null value determination on the field in the where clause. Otherwise, th
Optimization of SQL massive data query and non-use like processing solutions, data query like
1. To optimize the query, try to avoid full table scanning. First, consider creating an index on the columns involved in where and order.2. Try to avoid null value determination on the field in the where clause. Otherwise, the
How can I convert Oracle queries to queries in the SQL database? The following describes how to convert an Oracle query to an SQL query. If you are interested in Oracle query, take a look.
Oracle's TO_CHAR function can convert the n-bit NUMBER data type to the VARCHAR2 data
Select *from t1left join T2 on T2.sysno =t1. Asysnoleft join T3 on T3.sysno =t2. Asysnoleft join T4 on T4.sysno =t3. Asysnoleft join T5 on T5.sysno =t4. Asysnoleft join T6 on T6.sysno =t5. Asysnoleft join T7 on T7.sysno =t6. Asysnowhere t1.name like '%aaa% 'In the absence of any indexes, fuzzy queries, such SQL performance is the worst, such SQL for the Federated que
T-SQL dynamic query (1) -- Introduction
Preface:
During feature development, we often encounter a scenario similar to the following: the application has a query function that allows users to select the required conditions among many query conditions. This is also the focus of this series.
But sometimes you may find
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