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Many SQL programmers prefer to specify the column names in the INSERT INTO clause, whether or not it s necessary to do so, because it provides a method for documenting which columns are supposed to be receiving data. This practice also makes the INSERT statement less prone to errors and other problems should columns be added or the column order be changed at some future time. For these reasons, many organizations require the use of the column names in all INSERT statements.
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Now let s take a look at some examples of the INSERT statement. For these examples, I will use the CD_INVENTORY table. The table is based on the following table definition:
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CREATE TABLE CD_INVENTORY ( CD_NAME VARCHAR(60) NOT NULL, MUSIC_TYPE VARCHAR(15), PUBLISHER VARCHAR(50) DEFAULT 'Independent' NOT NULL, IN_STOCK INT NOT NULL );
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The first example I ll show you inserts values into every column in the CD_INVENTORY table:
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INSERT INTO CD_INVENTORY VALUES ( 'Patsy Cline: 12 Greatest Hits', 'Country', 'MCA Records', 32 );
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Notice that the INSERT INTO clause includes only the name of the CD_INVENTORY table, but does not specify any columns. In the VALUES clause, four values have been specified. The values are separated by commas, and the values with character string data types are
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enclosed in single quotes. If you refer back to the table definition, you ll see that the values specified in the VALUES clause are in the same order as the column definitions. When you execute the INSERT statement shown in the example, the data is added to the CD_INVENTORY table, as shown in Figure 8-1. If you had tried to execute an INSERT statement like the last example, but included only three values, rather than four, you would have received an error. For example, you would not be able to execute the following statement:
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INSERT INTO CD_INVENTORY VALUES ( 'Patsy Cline: 12 Greatest Hits', 'MCA Records', 32 );
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In this example, only three values have been specified. In this case, the missing value is for the MUSIC_TYPE column. Even though this column accepts null values, the SQL implementation has no way of knowing which value is being omitted, so an error is returned. Instead of leaving the value out of the VALUES clause, you can specify a null value, as shown in the following example:
INSERT INTO CD_INVENTORY VALUES ( 'Out Of Africa', null, 'MCA Records', 29 );
If you execute the INSERT statement, your table will now include an additional row. Figure 8-2 shows what the table would look like, assuming that the two INSERT statements have been executed. The null value was inserted into the MUSIC_TYPE column, and the other values were inserted into the appropriate columns. If a null value were not permitted in the MUSIC_TYPE column, you would have had to specify a value.
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Figure 8-2 shows the new row being inserted after the existing row in the table. However, the row might be inserted at any place in a table, depending on how the SQL implementation inserts rows. The SQL standard does not specify where a row should be inserted in a table. In fact, you should never rely on the rows in a table being in any particular order you should use the ORDER BY clause whenever the results of a SELECT need to be in a particular sequence.
Rather than having to provide a value for every column when you insert a row, you can specify which columns receive values. For example, you can specify values for the CD_NAME,
CD_NAME: VARCHAR(60) Patsy Cline: 12 Greatest Hits
MUSIC_TYPE: VARCHAR(15) Country
PUBLISHER: VARCHAR(50) MCA Records
IN_STOCK: INT 32
Figure 8-1
The CD_INVENTORY table with the new row of data
8:
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CD_NAME: VARCHAR(60) Patsy Cline: 12 Greatest Hits Out of Africa
MUSIC_TYPE: VARCHAR(15) Country NULL
PUBLISHER: VARCHAR(50) MCA Records MCA Records
IN_STOCK: INT 32 29
Figure 8-2
The CD_INVENTORY table with two rows of data
PUBLISHER, and IN_STOCK columns of the CD_INVENTORY table, as shown in the following example:
INSERT INTO CD_INVENTORY ( CD_NAME, PUBLISHER, IN_STOCK ) VALUES ( 'Fundamental', 'Capitol Records', 34 );
In this case, one value has been specified for each of the columns identified in the INSERT INTO clause, and the values are specified in the same order as the columns in the INSERT INTO clause. Notice that the INSERT statement doesn t include the MUSIC_TYPE column in the INSERT INTO clause or in the VALUES clause. You can omit this column because null values are permitted in that column. If you were to execute this statement, your CD_INVENTORY table would now have a third row (shown in Figure 8-3). Once again, the null value is automatically added to the MUSIC_TYPE column. If a default value had been defined for the column, that value would have been added. For example, the following INSERT statement omits the PUBLISHER column, rather than the MUSIC_TYPE column:
INSERT INTO CD_INVENTORY ( CD_NAME, MUSIC_TYPE, IN_STOCK ) VALUES ( 'Orlando', 'Soundtrack', 5 );
When the row is added to the CD_INVENTORY table, the default value (Independent) is added to the PUBLISHER column, as shown in Figure 8-4.
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