php database setting primary key

In PHP database, primary key is a very important concept. The primary key is the unique identifier of a record in the table. Using the primary key can quickly determine a record, and can also be used to connect tables. It is widely used in data query and table design.

This article will introduce how to set the primary key in the PHP database, related knowledge points and application scenarios, and how to use the primary key effectively.

1. What is the primary key?

In a relational database, each table has one or more columns, which can be used to uniquely identify a record. For example, a personnel information table contains employee numbers. Each employee number is unique and can uniquely identify an employee record. In this example, the employee number is the primary key of this table.

The primary key can be composed of one or more columns, but the value of the primary key column must be unique. The value of the primary key column cannot be NULL, because NULL cannot be used to uniquely identify a record.

2. Set the primary key

In the PHP database, you can use the following two methods to set the primary key:

1. Set the primary key when creating the table:

CREATE TABLE table_name (

column1 datatype PRIMARY KEY,
column2 datatype,
column3 datatype,

...
);

In this example, column1 is defined as the primary key.

2. Add a primary key to an existing table:

ALTER TABLE table_name
ADD PRIMARY KEY (column1);

In this example, the column1 column is defined as primary key.

Whether you set a primary key when creating a table or add a primary key to an existing table, you must ensure that the value of the primary key column is unique.

3. Application scenarios of primary keys

1. Ensure data uniqueness: By setting the primary key, you can ensure that the value of a column in the table is unique.

2. Connect multiple tables: When querying multiple tables, you can use primary keys to connect data between tables. For example, in a product table and an order table, the product id is the primary key of the product table and serves as a foreign key in the order table to connect the two tables.

3. Improve query efficiency: Using primary keys as query conditions can improve query efficiency. Because the value of the primary key is unique, the data that needs to be queried can be quickly located.

4. How to use primary keys effectively

1. Reasonable selection of primary key columns: Primary key columns should be unique, stable and simple. Uniqueness means that the value of the primary key column must be unique; stability means that the primary key column will not change during the life cycle of the record; simplicity means that the primary key column should be easy to understand, and do not use composite primary keys or primary keys that are too long.

2. Use appropriate data types: The data type of the primary key column should be a smaller data type. Do not choose a large data type, because this will take up more storage space and query time.

3. Avoid frequent updates of primary key columns: Frequent updates of primary key columns will affect performance because the updates will cause index reconstruction. If records need to be modified frequently, consider using non-primary key columns as update conditions.

4. Index optimization: The primary key column is usually used as an index, and query efficiency can be improved by optimizing the index. Consider using strategies such as covering indexes or clustered indexes to optimize query performance.

5. Summary

In PHP database, primary key is a very important concept. It can be used to uniquely identify a record, connect multiple tables, and improve query efficiency. When setting the primary key, you need to pay attention to selecting the appropriate primary key column and data type, avoid frequently updating the primary key column, and perform index optimization and other operations to improve query efficiency and reduce resource consumption.

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