find duplicates query sql

SQL Multiple primary key tables, when the inserted data is duplicated, are prompted to violate the primary KEY constraint that cannot be inserted by the error. So, how do I find duplicate values for the inserted data? Workaround: Use Group bySuppose there is a table #a , there are saleid,vendorid,comid,price,saleprice,quantity and other fields. The primary key is: Saleid,vendorid,comid three of them. Assu

Tags: sql"Find employee records for the second highest wage in the employee table" How to write the SQL statementThis query first finds the highest wage, then excludes it from the list and then finds the highest wage. It was clear that the second return was the second highest wage.Select top 1 * from employee where sal

to be linked. ON: Specifies the fields shared by these tables. Specify the connection conditions based on the primary key and external key of the table. The ANSI link syntax is as follows: SELECT table_name.column_name, table_name.column_name ,...... FROM {table_name [join_type] JOIN table_name ON search_conditions} WHERE [search_conditions] [Join_type] can be in the following three keywords: INNER (inner join): the link query result contains only th

overloaded, as follows: Public Static This where class; We use the Fromsql overloaded method above to pass string parameters, while adding a database table operation to the query string to verify that EF core prevents SQL injection. using(varContext =NewEfcoredbcontext ()) { varSearchString ="Jeffcky; DROP TABLE dbo. Blogs;"; varBlogs =context. Blogs. Fromsql ("SELECT Id, Nam

repeated records and its name attributeGroup by numHaving count (Num)> 1 -- group by num to find the num column in the table, that is, more than onceDelete data:Delete from studentGroup by numHaving count (Num)> 1In this way, all duplicates are deleted. 3. Use the distinct method-Useful for small tables Create Table table_new as select distinct * From Table1 minuxTruncate table Table1;Insert into Table1 se

, SQL Server uses three methods to implement this grouping, and the first one requires your assistance: Happy to find data series that have been pre-categorized by the component group. by executing a set of data Hash operation. Sorts the order in which the data is grouped. Pre-classificationThe index of the pre-categorized data is your way, that is, a frequent sequence of

example: Tag table:{tag_id, tag_name, links} (can actually regard links as a manual index)2, maintenance of this tag table is more troublesome, in consideration of efficiency, generally will be timed to the links field to do a full table update (for frequent insertion or deletion of records of the news table, can be early every day, to the full record set of tags to do the number of citations and update the links field)3, constructs the dynamic multi-layered

Linux platform, we generally through the top command to see the most performance-consuming process, if the see is Oracle, then we need to pass the process number, query the process currently executing SQL statements, Baidu Online has a lot of SQL, I generally find by the following way:find the SID of the corresponding

heap table, that is, there is a clustered index entry, well, SQL Server is easy to find its pre-reading reference: statistical information.Also, we know that the data is stored in b-tree numbers, and the data pages that are read are present with the leaf nodes. So basically there is no continuous reading of the gratitude.A leaf node is a data page, and a data page is a pre-read.Let's look at an example:We

Find an SQL statement ~ ''' Delphi/Windows SDK/API Http://www.delphi2007.net/DelphiDB/html/delphi_20061220134634201.html I have three tables: AA. BDF BB. DBF cc. DBF Fields in AA. DBF Jh yc Yx yxh Name1 ch 0.2 101.1 Fields in BB. DBF Using jd1 jd2 Name 1 100.1 200.1 Fields in CC. DBF JH HS Name 1 20061011 0.3 I want to complete this query: First, I want to ad

A Query method thinkphp provides three basic query methods: String conditional query, indexed array condition query, and object bar Query. In most cases, it is recommended to use indexed arrays and object methods as query criteria

Label:The first approach: querying using system tables--replace text with the one you want to find. Select name from sysobjects o, syscomments s where o.id = S.id and the text like '%text% ' and O.xtype= ' P ' xtype: Object type. Can be one of the following types of objects: C = CHECK Constraint D = default value or defaults constraint F = FOREIGN key constraint L = log FN = scalar function IF = inline table function P = stored procedure PK = PRIMARY

deptno=10), query table with the same staff with department Number 10 The name, work, salary, department number of the worker. Because there are multiple rows in the returned result, the subquery is concatenated with "in".In and exists: exists () the subquery that follows is called the correlated subquery, which is not the value of the returned list. Just returns the result of a ture or false, which runs the main

silent unlocked unlocked unlocked not locked NOLOCK unlocked unlocked unlocked HOLDLOCK shared share share update UPDLOCK error update update TABLOCKX error Unlocked not Lock update other unlocked unlocked Unlocked update * Specifies that the NOLOCK hint will make the table specified with this hint read-only in cursor. 16. Use Profiler to track the query, get the time required to query,

For example, if a table is like this, the ID is the primary key and the table is auto-incrementing: Column name: Id Columna columnb columnc Column value: 1 A asdfd afdsf 2 B sdfafsd 080dfs 3 A dfsafja08 90879. 4 C fds934 fsdaf 5 B safsfsd fd86fsdaf The query results after the SQL statement is executed are as follows: Column name: Id Columna columnb columnc Column value: 1 A asdfd afdsf 2 B sdfafsd 080dfs Th

operands, which can be an arithmetic operator, an assignment operator, a bitwise operator, a comparison operator, a logical operator, a string concatenation operator, a unary operatorThe SQL statement that queries the LIKE operator needs to use the following wildcard operator:For example, if you want to find the first two digits of the phone number in the Employee Information table as "13", you can write t

selected. Then the data can be extracted with limit. SELECT * FROM Employees ORDER by ID (field name) DESC/ASC limit x (extract quantity) Select * from Order by desc 0,1 Select * from Order by desc 1 Both of these methods are the same result (only for the above query criteria). when there is more than one data, the initial value of the fetch position becomes a different result. Environment II : Number of people at the latest date of ent

sets, but consumes system resources and should be changed to this: CREATE TABLE#T (...)13, many times use exists insteadinchis a good choice: Select num fromA Where numinch(Select num fromb) Replace with the following statement: Select Num fromA Where exists (select 1 fromb where num=a.num)14, not all indexes are valid for queries, SQL is query-optimized based on the data in the table, and when there is a

This article from: http://www.cnblogs.com/smailxiaobai/archive/2012/01/16/2323291.htmlSpecifies a temporary named result set, which is called a common table expression (CTE). The expression originates from a simple query and is defined within the execution scope of a single SELECT, INSERT, UPDATE, or DELETE statement. This clause can also be used in the CREATE VIEW statement as part of the statement's SELECT definition statement. A common table expres

(SELECT DISTINCT job from EMP where deptno=10), query table with the same staff with department Number 10 The name, work, salary, department number of the worker. Because there are multiple rows in the returned result, the subquery is concatenated with "in".In and exists: exists () the subquery that follows is called the correlated subquery, which is not the value of the returned list. Just returns the result of a ture or false, which runs the main