6.1. Inserting Data

6.1. Inserting Data

6.1.插入数据

When a table is created, it contains no data. The first thing to do before a database can be of much use is to insert data. Data is conceptually inserted one row at a time. Of course you can also insert more than one row, but there is no way to insert less than one row. Even if you know only some column values, a complete row must be created.

表创建的时候，没有数据。在使用数据库之前的第一件事，是插入数据。从概念上讲，数据一次只能插入一行。当然，您也可以插入多行，但是无法插入少于一行。即使您只知道某几个列的值，但插入的时候也必须创建完整的行。

To create a new row, use the INSERT command. The command requires the table name and column values. For example, consider the products table from Chapter 5:

使用INSERT命令创建行。该命令需要有表名和列值。例如，假设表products如下：

CREATE TABLE products (

product_no integer,

name text,

price numeric

);

An example command to insert a row would be:

插入一行数据的示例如下：

INSERT INTO products VALUES (1, 'Cheese', 9.99);

The data values are listed in the order in which the columns appear in the table, separated by commas.Usually, the data values will be literals (constants), but scalar expressions are also allowed.

列值以逗号分隔，按照表列的顺序排列。通常，数据值应该是常量，但范围表达式也可以。

The above syntax has the drawback that you need to know the order of the columns in the table. To avoid this you can also list the columns explicitly. For example, both of the following commands have the same effect as the one above:

上例语法有个缺点，就是你必须知道表的列顺序。可以通过显式的指定表名来解决此问题。例如，以下两个命令均可以实现上例中的效果：

INSERT INTO products (product_no, name, price) VALUES (1, 'Cheese',9.99);

INSERT INTO products (name, price, product_no) VALUES ('Cheese',9.99, 1);

Many users consider it good practice to always list the column names.

很多用户更倾向于在插入数据的时候列出表名。

If you don't have values for all the columns, you can omit some of them. In that case, the columns will be filled with their default values. For example:

如果你没有针对所有列的值，那么可以忽略这些列。这样，列会被其默认值填充，例如：

INSERT INTO products (product_no, name) VALUES (1, 'Cheese');

INSERT INTO products VALUES (1, 'Cheese');

The second form is a PostgreSQL extension. It fills the columns from the left with as many values as are given, and the rest will be defaulted.

第二个格式是PostgreSQL特有的。它会根据给定值的个数，从左填充到列中，剩余的列填充默认值。

For clarity, you can also request default values explicitly, for individual columns or for the entire row:

为了清楚一些，也可以显式的指定为某列或所有列插入默认值：

INSERT INTO products (product_no, name, price) VALUES (1, 'Cheese',DEFAULT);

INSERT INTO products DEFAULT VALUES;

You can insert multiple rows in a single command:

也可以在一个命令中插入多行：

INSERT INTO products (product_no, name, price) VALUES

(1, 'Cheese', 9.99),

(2, 'Bread', 1.99),

(3, 'Milk', 2.99);

It is also possible to insert the result of a query (which might be no rows, one row, or many rows):

也可以将查询结果插入表中（可能没有数据，一行或多行）：

INSERT INTO products (product_no, name, price)

SELECT product_no, name, price FROM new_products

WHERE release_date = 'today';

This provides the full power of the SQL query mechanism (Chapter 7) for computing the rows to be inserted.

这提供了SQL查询机制（第7章）的全部功能，用于计算要插入的行。

Tip

小贴士

When inserting a lot of data at the same time, consider using the COPY command. It is not as flexible as the INSERT command, but is more efficient. Refer to Section 14.4 for more information on improving bulk loading performance.

可以考虑使用COPY命令同时插入大量数据。虽然不如 INSERT命令灵活，但比其高效。关于如何提高大批量加载的性能的更多信息，请参见14.4节。

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