prepare() and execute*() give you more power and flexibilty for query execution. Prepare/execute mode is helpful when you have to run the same query several times but with different values in it, such as adding a list of addresses into a database.
Another place prepare/execute is useful is supporting databases which have different SQL syntaxes. Imagine you want to support two databases with different INSERT syntax:
db1: INSERT INTO tbl_name (col1, col2) VALUES (expr1, expr2) db2: INSERT INTO tbl_name SET col1=expr1, col2=expr2 |
$statement['db1']['INSERT_PERSON'] = 'INSERT INTO person (surname, name, age) VALUES (?, ?, ?)'; $statement['db2']['INSERT_PERSON'] = 'INSERT INTO person SET surname=?, name=?, age=?'; |
To use the features above, you have to do two steps. Step one is to prepare the statement and the second is to execute it.
To start out, you need to prepare() a generic SQL statment. Create a generic statment by writing the SQL query as usual:
SELECT surname, name, age FROM person WHERE name = 'name_to_find' AND age < age_limit |
SELECT surname, name, age FROM person WHERE name = ? AND age < ? |
prepare() can handle different types of placeholders (a.k.a. wildcards).
? - (recommended) stands for a scalar value like strings or numbers, the value will be quoted depending of the database |
! - stands for a scalar value and will inserted into the statement "as is". |
& - requires an existing filename, the content of this file will be included into the statment (i.e. for saving binary data of a graphic file in a database) |
Use backslashes to escape placeholder characters if you don't want them to be interpreted as placeholders:
UPDATE foo SET col=? WHERE col='over \& under' |
After preparing the statement, you can execute the query. This means to assign the variables to the prepared statement. To do this, execute() requires two arguments: the statement handle returned by prepare() and a scalar or array with the values to assign.
Example 26-1. Passing scalars to execute()
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When a prepared statement has multiple placeholders, you must use an array to pass the values to execute(). The first entry of the array represents the first placeholder, the second the second placeholder, etc. The order is independent of the type of placeholder used.
Example 26-2. Passing an array to execute()
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DB contains a process for executing several queries at once. So, rather than having to execute them manually, like this:
Example 26-3. Passing arrays to execute()
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INSERT INTO numbers VALUES ('1', 'one', 'en') INSERT INTO numbers VALUES ('2', 'two', 'to') INSERT INTO numbers VALUES ('3', 'three', 'tre') INSERT INTO numbers VALUES ('4', 'four', 'fire') |
Example 26-4. Using executeMultiple() instead of execute()
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The result is the same. If one of the records failed, the unfinished records will not be executed.
execute*() has three possible returns: a new DB_result object for queries that return results (such as SELECT queries), DB_OK for queries that manipulate data (such as INSERT queries) or a DB_Error object on failure