postgres join types

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Four types of SQL connections: left Outer Join, right Outer Join, inner join, and full join

a. *, B. * from a inner join B on A. ID = B. parent_idThe result is1 piece 3 1 23 12 Li Si 2 34 22) left joinSelect a. *, B. * from a left join B on A. ID = B. parent_idThe result is1 piece 3 1 23 12 Li Si 2 34 23 Wang Wu null 3) Right joinSelect a. *, B. * from a right join B on A. ID = B. parent_idThe result is1 piece 3 1 23 12 Li Si 2 34 2Null 3 34 44) full

Difference between four types of SQL connections: left Outer Join, right Outer Join, full join, and inner join

? The connection conditions can be specified in the from or where clause. We recommend that you specify the connection conditions in the from clause. The where and having clauses can also contain search conditions to further filter the rows selected by the connection conditions. Connections can be divided into the following types: Internal Connection.(Typical join operations use comparison operators such a

Postgres database three types of speed comparison for creating statements

Number of records in table: 1578463 Select COUNT (*) from Reorder_guideline; Count---------1578463 (1 Row Records) 2. three statements creating tables CREATE TABLE: (1) most commonly used (23171.485ms) A1stream_db=> CREATE table reorder_guideline_2 as table reorder_guideline; Time: 23171.485 ms (2) with unlogged logo (1734.085ms) Create unlogged table reorder_guideline_2 as table reorder_guideline; Time: 1734.085 ms (3) temporary table with temp ID (1666.934ms) Create temp table reorder_gu

Seven types of join in MySQL and seven types of join in mysql

Seven types of join in MySQL and seven types of join in mysqlCreate a table Here we will first create two tables with foreign key associations. Create database db0206; USE db0206; create table 'db0206 '. 'tbl _ dept' ('id' INT (11) not null AUTO_INCREMENT, 'deptname' VARCHAR (30), 'locadd' VARCHAR (40 ), primary key ('

Database Join types

". Description: The left table is the table to the left of the "(OUTER JOIN)" keyword. The right table is, of course, on the right. In three types of outer joins, the OUTER keyword can be omitted.The following example illustrates: statement 5: Left OUTER join (OUTER join) SELECT,o.order_number,o.customer_id,,c

Three types of SQL Join

to reduce the size of the hash table, the hash value can be quickly compared. If both tables are large, then the hash match jion is very inefficient compared to other types of joins.A Hash Match join is very efficient for large datasets, especially one that is much smaller than the other. The hash match join is also a very effective way to do this if the table i

Mysql: 21 best practices for performance optimization 5 [using equivalent types of _ MySQL during Join tables

Mysql: 21 best practices for performance optimization 5 [use and index equivalent columns when joining a table] When you Join a table, use a column of equivalent type and index it. If your application has many JOIN queries, you should confirm that the Join fields in the two tables are indexed. In this way, MySQL will launch a mechanism to optimize th

Use the Join () method in Python to merge and stitch elements in various data types

" Connector characters ". Join (list or tuple or string or dictionary)Returns a string that is spliced with a connectorIf the object is a list, tuples are spliced in a subscript elementIf the object is a string, it is a word element that is spliced in unitsIf the object is a dictionary, it is stitched in a single key unitListIn [4]: a = ["123""123"]in ["". Join (a) In [6]: bout['123123'DictionaryIn []: a =

Seven types of Join for MySQL

Create a tableFast to the endStudent tableCreate TableStudent (IDint( One) not NULLauto_increment, namevarchar( -), Addressvarchar( +), Primary Key(ID)) engine=InnoDB CharSet=UTF8;INSERT intoStudent (name,address)VALUES('Tiankai Zhi','Tianchang, Anhui province');INSERT intoStudent (name,address)VALUES('Tau','Tongling, Anhui province');INSERT intoStudent (name,address)VALUES('Shi Dongdong','Anqing, Anhui province');INSERT intoStudent (name,address)VALUES('Wei Zhong Original','Chuzhou, Anhui

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