select from two tables sql without join

Nner Join joins two tables, three tables, five tables of SQL statements2013-04-14 15:13: 11来 Source: West e-Net SQL INNER join keyword indicates that the INNER

SQL statement Optimization-query different rows of the two tables NOT IN, NOT EXISTS, Join query Left Join, existsleft In actual development, we often need to compare the differences between two or more tables and compare the data that is the same and the data is different.

(1) Cross join is what we call the Cartesian product. Query the number of records that satisfy both tables, A (3 Records), B (9 Records), A*b (27 records).For example: An employee table (hr.employees) and a freight company (sales.shippers) table make a cross-connection.1 SELECT * FROM hr.employees;2 select * from Sal

Tags: Connection Method field name comparison field record right outer connection outer JOIN mode use 1-- inner connection: INNER JOIN It represents a matching record that returns two tables or Recordset join fields, representing the portions of the two tables that are cont

TableB W Here Tablea.id=tableb.id (after cross joins can only be used where not on)three. Cross-connectConcept: A cross join without a where condition will produce the Cartesian product involved in the join table. That is, the result set of the number of rows *tableb the TableA number of rows. (TableA 3 Rows *tableb 3 rows =9 rows) SQL statement:

finally found on Wikipedia as an argument.SQL defines two different syntax ways to represent "connections." The first is the explicit join symbol, which uses the keyword explicitly, followed by JOIN the implicit join symbol, which uses the so-called implicit join symbol. The implicit

. Method Three: Using connection query Connection queries include: 1. Self-connect (join equals inner JOIN): Query result is data that exists on both sides 2. Left join to the left join: return all data on the right, return to the back, null not present 3. Right join: Retu

Label:First, the basic SELECT statement 1. "*" NOTE: In the SELECT statement, use * To select all the columns, this is a habit should be resisted. While it saves time to enter column names, it also means more data is available than is really needed. Correspondingly, the performance and network performance of the application can be reduced. A good rule is to

I. Basic select statements 1. Note for "*": In the SELECT statement, use * to select all columns, which should be resisted. Although saving the time for entering the column name, it also means that the data obtained is much more than the data actually needed. Correspondingly, it will also reduce the application performance and network performance. A good rule is

SQL statements (a couple of tables together to query, get the first few to the more than 10 data): 1. If there are a,b,c,d four tables, a,b,c,d are linked together as follows: The ((A Inner join B By A.Id =B.AId) Inner join C By B.Id =C.BId)Inner

The use of ExistsSelect *from haha where exists (select *from bumen where Bumen.code = haha.bumen and bumen.name = ' Sales department ') and AGE>35(Run method is query-by-clause)Select Name,sex,age, (select name from bumen where Bumen.code = haha.bumen) as department from hahaSelect Name,sex,age, (select name from bume

Table:Person+-------------+---------+| Column Name | Type |+-------------+---------+| PersonId | int | | FirstName | varchar | | LastName | varchar |+-------------+---------+personid is the primary key, column for this table.Table:Address+-------------+---------+| Column Name | Type |+-------------+---------+| Addressid | int | | PersonId | int | | City | varchar | | State | varchar |+-------------+---------+addressid are the primary key column for thi

sides2. Left join to the left join: return all data on the right, return to the back, null not present3. Right join: Return all data on the right, return on left, no null4. Fully connected full join: Returns if one of the tables exists and the other does not exist as Nul

aliases for Sno and sname in the student table, for example:2. Add aliases to the tableSelect Empno, ename from EmpaThe original table name EMP is changed to alias a? Example 5: According to the existing student table and SC table, query the student scores of the S001 school number.Solution: Query the Student table and SC table information first. For example, with:Watermark/2/text/ahr0cdovl2jsb2cuy3nkbi5uzxqv/font/5a6l5l2t/fontsize/400/fill/i0jbqkfcma==/dissolve/70/gravity /center "/>Two more f

ArticleDirectory 1. Example of replacing inner join with exists: When using exists, if you can use it correctly, it may increase the query speed: 1. Replace inner join with exists 2. Replace in with exists 1. Example of replacing inner join with exists: When writing SQL statements, you may encou

Query the username, psw, gname, and Tel of all realnames today. Table Structure: Table T1 Field name: t1_id, username, psw Table T2 Field name: t2_id, gname, t1_id // here one t1_id corresponds to multiple t2_id T3 Field name: t3_id, realname, tel, t1_id // here, a t1_id corresponds to a t3_id The trouble is that when a realname has no content in Table T2, the username, psw, and Tel of this realname should be displayed and used directly. SQL

the same as that in the previous example! 4: Inner join or join; It is the record that the returned field ID exists in both the table votemaster and voter.5: Cross join (full join) with no where Condition A cross join without a where clause will generate the Cartesian produ

SELECT * FROM table1 inner join table2 on Table1.id=table2.idIn fact INNER JOIN ... The syntax format for on is summarized as follows:From ((Table 1 INNER join table 2 on table 1. Field number = Table 2. Field number) INNER join table 3 on table 1. Field number = Table 3. Fi

Query the username, psw, gname, and tel of all realnames today.Table Structure:Table t1Field name: t1_id, username, pswTable t2Field name: t2_id, gname, t1_id // here one t1_id corresponds to multiple t2_idT3Field name: t3_id, realname, tel, t1_id // here, a t1_id corresponds to a t3_idThe trouble is that when a realname has no content in Table t2, the username, psw, and tel of this realname should be displayed and used directly.SQL = "select username

fromSales S Join stores asT on s.stor_id=t.stor_id3 GROUP BY T.state,t.stor_name4 ORDER BY totalsales Desc5 6 SelectTop1T.state,t.stor_name,sum (S.qty) asTotalSales7 fromSales S Join stores asT on s.stor_id=t.stor_id8 GROUP BY T.state,t.stor_name9ORDER BY totalsales DescView CodeDerived tablesSelect can also use derived tables (subqueries), also known as logic