sql query compare two columns same table

displayed, then, use the values of the columns in the left table to match the right table. If the value of the Left table cannot be found, null is used to fill in the values of rows in the right table that do not match in the result set. The statement for implementing the l

Usage scenarios:For example, you need to query all student numbers with scores greater than 95, separated by commas into a string, from the Student score table.To prepare the test data:CREATE TABLE score (ID int,score int)INSERT into score values (1,90)INSERT into score values (2,96)INSERT into score values (3,99)It is now necessary to query the result string "2,

connection statementsOf course, the above two tables are a one-to-one relationship, so how do we write a concatenated SQL statement if Table A and table B are a pair of many, many pairs, or many to many?In fact, two tables of SQL statements and one-to-one SQL statements are

connection statementsOf course, the above two tables are a one-to-one relationship, so how do we write a concatenated SQL statement if Table A and table B are a pair of many, many pairs, or many to many?In fact, two tables of SQL statements and one-to-one SQL statements are

Tags: must result basic usage start without retrieving ROM start sibling nodeUsually use the self-related tree structure table to store the data of the tree structure, the hierarchical relationship between the data represents the parent-child relationship in the tree structure, and is usually described by the relation between the two columns in the table, such as

table As a table example select E.emono,e.ename from (SELECT * from where deptno=30) E gave the table an alias E As a condition there are several situations Single-column: You can use =,>, A multiline column (collection) can be Single-row multi-column (object) is a row, like an object, what property has Multiline multiple

1. It is a sub-database rather than a sub-table, which requires consideration of the introduction of a sub-table algorithm, but also affects subsequent queries.2. Thermal data is only part of the total data, so every time we first query the hot library, the following conditions only query cold storage--a. When the

table, and when there is no matching row in one table, the selection list column of the other table contains a null value (NULL) if there is one, all data is displayedSQL syntax:Select *from table1 full join table2 on table1. Condition column name = table2. Condition Column NameInternal connection:Concept: An inner join is a comparison operator that compares the

sp_configure ' xp_cmdshell ', 1 Reconfigure DECLARE @cmd NVARCHAR (4000) = ' bcp ' + @Columns + ' Union all ' + @Data + ' "queryout ' + @FilePath + '-c-t ' PRINT @cmd EXEC Sys.xp_cmdshell @cmd EXEC sp_configure ' xp_cmdshell ', 0 Reconfigure EXEC (' DROP TABLE ' + @tmp) End TRY BEGIN CATCH --Handling exceptions IF object_id (' tempdb ... ') + @tmp) is not NULL EXEC (' DROP

-many SQL statements of the two tables are similar to those of the one-to-one SQL statement, but the query results are different. Of course, the two tables must be slightly changed.For example, the column in table 1 can be changed:Sno Name CnoThe columns in

The JOINS type and its syntaxNatural joins (natural connection):–natural JOIN clause–using clause–on clauseSelf-connectNon-equivalent connectionOuter joins (external connection):–left OUTER join (left OUTER join)–right OUTER join (right outer join)–full OUTER join (full outer join)Cartesian product–cross Join (Cross Connect)Grammar:Select Table1.column, Table2.columnFrom table1[Natural Join table2] |[Join Table2 using (column_name)] |[Join Table2On (table1.column_name = table2.column_name)]|[Lef

Multi-table Query SQL statement1--Unlock Scott users 2 alter userScott account unlock 3--Retrieves the specified column 4 select Job,ename,empno fromEmp 5--With expression Yes SELECT clause 6 select sal* (1+0.2), Sal fromEmp 7--Show non-repeating records 8 select distinct job fromEmp 9--Comparison filter ; Select Empno,ename,job fromEMP;12 Select Empno,ename,sal

: 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

Label:In the database, there is a certain connection between the tables, if you need to make a series of queries on the data, it is not enough to get the data information from a table or a library, it is necessary to extract the required data from multiple tables or multiple databases, and some simple SELECT statement query is unable to meet the needs of users. At this point, you need to refer to advanced q

How can we query the information of different tables together when we talk about the inefficiency of the related sub-queries in the previous blog post? This requires a table join.Unlike the previous union query, the Union combines different tables, that is, vertical joins, which are spelled upright.A table join is a ho

SQL Server1. Query All TablesSelect [ID], [name] from [sysobjects] where [type] = ' u ' ORDER by [name]2. Query all databasesSelect [Name] from [sysdatabases] ORDER by [name]3. Query the fields in the tableSelect [Name] from [syscolumns] where [name] = ' tablexxx ' ORDER by [Colid]Oracle1 . Find all indexes of the

Label:Transferred from: http://www.cnblogs.com/aflyfly/archive/2011/08/10/2133546.html actinium Fly MS SQL Server1. Query All TablesSelect [ID], [name] from [sysobjects] where [type] = ' u ' ORDER by [name]2. Query all databases3. Select [Name] from [sysdatabases] ORDER by [name]Querying fields in a tableSelect [Name] from [syscolumns] where [name] = ' tablexxx '

Tags: --sql Server 2005, or 2012:select * from Information_schema.tables--sql server 2000:select * from sysobjects WHERE xt ype= ' u ' select * from sysobjects WHERE xtype= ' u ' select table_name from GEOVIDNU. Information_schema. Tablesselect sobjects.namefrom sysobjects sobjectswhere sobjects.xtype = ' U ' EXEC sp_spaceused ' yourtablename '-- The column names of all watches are shown in select Column_n

Label:MS SQL Server 1, querying all tables select [ID], [name] from [sysobjects] where [type] = ' u ' ORDER BY [name] 2, querying all Databases 3, select [Name] F ROM [sysdatabases] ORDER BY [Name] Query table field select [Name] from [syscolumns] where [name] = ' tablexxx ' ORDER by [Colid] Oracle 1. Find all indexes of the