How To Write Case Statement In Sql

The complete collection of SQL statement operations deserves to be permanently stored the following statements are part of the MSSQL statement and are not available in Access. SQL classification: ddl-data Definition language (create,alter,drop,declare) dml-Data Manipulation Language (Select,delete,update,insert) dcl-Data Control Language (Grant,revoke, Commit,rollback first, briefly introduce the basic statement: 1, Description: Create number ...

For a lot of news at home and abroad, BBS and E-commerce sites are used asp+sql design, and write ASP programmers Many (there are a lot of just graduated), so, Asp+sql attack success rate is also relatively high. This kind of attack method has little to do with the NT version and the SQL version. There is no corresponding patch, because the loophole is caused by the programmer, and most of the book on ASP programming, the source code example has this flaw exists, in fact, just some legitimate ASP on the request of SQL, leaving endless trouble! A This attack method originated from ...

MySQL database sql statement commonly used optimization methods 1. Query optimization, should try to avoid full table scan, should first consider where and order by the columns involved in the establishment of the index. 2. Should be avoided in the where clause on the field null value judgment, otherwise it will cause the engine to abandon the use of indexes and full table scan, such as: select id from t where num is null You can set the default value of num 0, to ensure that Num column table does not null value ...

We want to do not only write SQL, but also to do a good performance of the SQL, the following for the author to learn, extract, and summarized part of the information to share with you! (1) Select the most efficient table name order (valid only in the Rule-based optimizer): The ORACLE parser processes the table names in the FROM clause in Right-to-left order, and the last table in the FROM clause (the underlying table driving tables) is processed first, In the case where multiple tables are included in the FROM clause, you must select the table with the least number of records as the underlying table. If...

SQL used to manipulate the database is generally divided into two kinds, one is the query, which is what we call the SELECT statement, the other is to update the statement, also known as data manipulation statements. The implication is to modify the data. There are 3 statements in the standard SQL, which are INSERT, UPDATE, and DELETE. There is another REPLACE statement in MySQL, so this article uses MySQL as a background to discuss how to make updates in SQL. First, INSERT and REPLACE I ...

Intermediary transaction http://www.aliyun.com/zixun/aggregation/6858.html ">seo diagnose Taobao guest cloud host technology Hall before writing a paging stored procedure, we first create a test table for the database. This test shows that there are 3 fields, called Order, which are or_id,orname,datesta; The following creates a table script: CREATE TABLE [dbo]. [Orders ...]

Intermediary transaction http://www.aliyun.com/zixun/aggregation/6858.html ">seo diagnose Taobao guest cloud host technology Hall in the consideration of a website if the host million or tens of millions of PV, We tend to think in two directions instinctively: static and distributed. Of course, for Sina and other portal types of Web sites, static + read and write separation and distribution, can solve most of the problems. But we are facing more, may be large data + high and ...

Setting filter conditions to improve indexing efficiency good indexes are key to SQL Server database performance, but efficient indexes are carefully designed. As we all know, a primary key is a unique identifier for a data object, and if there is no clustered index in the datasheet, the SQL Server database will create a clustered index (Clustered index) for the primary key by default in order to maintain the uniqueness of the key. Unless the user specifically specifies that the index should be created as a nonclustered index (non-clustered index). There is no doubt that we ...

A few suggestions to improve SQL execution efficiency: Try not to include subqueries in where; queries about time, try not to write: where To_char (dif_date, ' yyyy ') =to_char (' 2007-07-01 ', ' yyyy '); In the filter condition, the condition in which the maximum number of records can be filtered must be placed at the end of the WHERE clause, and the last table (underlying table, driving table) in the FROM clause will be first ...

To realize the problem of importing massive data, import millions of data into SQL Server one at a time, and if you write with a normal INSERT statement, I'm afraid it won't be completed in a few hours, first consider using bcp, but it's based on the command line, and it's too unfriendly for the user to actually use ; finally decided to use the BULK INSERT statement implementation, BULK Insert can also achieve large amount of data import, and can be implemented programmatically, the interface can be done very friendly, it is very high speed: Import 1 million data ...