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This article mainly introduces "the use of database inner join statements and matters needing attention". In daily operation, I believe that many people have doubts about the use of database inner join statements and matters needing attention. Xiaobian consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts about the use of database inner join statements and matters needing attention. Next, please follow the editor to study!

Inner join (equivalent join): only rows with equal join fields in two tables are returned.

Left join (left join): returns records that include all records in the left table and records that are equal to join fields in the right table.

Right join (right join): returns records that include all records in the right table and records that are equal to join fields in the left table.

INNER JOIN syntax:

The use of INNER JOIN to join two data tables:

SELECT * FROM Table 1 INNER JOIN Table 2 ON Table 1. Field number = Table 2. Field number

The use of INNER JOIN to connect three data tables:

1 SELECT * 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. Field number

The use of INNER JOIN to join four data tables:

SELECT * 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. Field number) INNER JOIN Table 4 ON Member. Field number = Table 4. Field number

The use of INNER JOIN to connect five data tables:

SELECT * 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. Field number) INNER JOIN Table 4 ON Member. Field number = Table 4. Field number) INNER JOIN Table 5 ON Member. Field number = Table 5. Field number

The use of joining six data tables: slightly, similar to the above join method, let's give an example.

Note:

In the process of entering letters, be sure to use English half-corner punctuation, leaving half-corner space between words.

When creating a data table, if a table is joined to more than one table, the fields in that table must be of the numeric data type, while the same fields in the multiple tables must be the primary key and the automatic numbering data type. Otherwise, it will be difficult to connect successfully.

Code nesting fast method: for example, if you want to join five tables, just add a parenthesis before and after the code that connects the four tables (parentheses are added after FROM, and parentheses are added at the end of the code), and then continue to add "INNER JOIN table name X ON Table 1. Field number = Table X. field number" code after the parentheses, so you can join the data table indefinitely. )

At this point, the study on "the use of database inner join statements and matters needing attention" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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