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><A
NAME="DML-INSERT"
>6.1. Inserting Data</A
></H1
><P
> 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.
</P
><P
> To create a new row, use the <A
HREF="sql-insert.html"
>INSERT</A
>
command. The command requires the
table name and column values. For
example, consider the products table from <A
HREF="ddl.html"
>Chapter 5</A
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE products (
product_no integer,
name text,
price numeric
);</PRE
><P>
An example command to insert a row would be:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO products VALUES (1, 'Cheese', 9.99);</PRE
><P>
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.
</P
><P
> 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:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO products (product_no, name, price) VALUES (1, 'Cheese', 9.99);
INSERT INTO products (name, price, product_no) VALUES ('Cheese', 9.99, 1);</PRE
><P>
Many users consider it good practice to always list the column
names.
</P
><P
> 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:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO products (product_no, name) VALUES (1, 'Cheese');
INSERT INTO products VALUES (1, 'Cheese');</PRE
><P>
The second form is a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
extension. It fills the columns from the left with as many values
as are given, and the rest will be defaulted.
</P
><P
> For clarity, you can also request default values explicitly, for
individual columns or for the entire row:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO products (product_no, name, price) VALUES (1, 'Cheese', DEFAULT);
INSERT INTO products DEFAULT VALUES;</PRE
><P>
</P
><P
> You can insert multiple rows in a single command:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO products (product_no, name, price) VALUES
(1, 'Cheese', 9.99),
(2, 'Bread', 1.99),
(3, 'Milk', 2.99);</PRE
><P>
</P
><P
> It is also possible to insert the result of a query (which might be no
rows, one row, or many rows):
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO products (product_no, name, price)
SELECT product_no, name, price FROM new_products
WHERE release_date = 'today';</PRE
><P>
This provides the full power of the SQL query mechanism (<A
HREF="queries.html"
>Chapter 7</A
>) for computing the rows to be inserted.
</P
><DIV
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><BLOCKQUOTE
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><P
><B
>Tip: </B
> When inserting a lot of data at the same time, considering using
the <A
HREF="sql-copy.html"
>COPY</A
> command.
It is not as flexible as the <A
HREF="sql-insert.html"
>INSERT</A
>
command, but is more efficient. Refer
to <A
HREF="populate.html"
>Section 14.4</A
> for more information on improving
bulk loading performance.
</P
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