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sqlite_create_aggregateSQLiteDatabase::createAggregateRegister an aggregating UDF for use in SQL statements Description
void sqlite_create_aggregate
( resource
$dbhandle
, string $function_name
, callable $step_func
, callable $finalize_func
[, int $num_args = -1
] )Object oriented style (method):
public void SQLiteDatabase::createAggregate
( string
$function_name
, callable $step_func
, callable $finalize_func
[, int $num_args = -1
] )sqlite_create_aggregate is similar to sqlite_create_function except that it registers functions that can be used to calculate a result aggregated across all the rows of a query.
The key difference between this function and
sqlite_create_function is that two functions are
required to manage the aggregate; Parameters
Return ValuesNo value is returned. Examples
Example #1 max_length aggregation function example
<?php
In this example, we are creating an aggregating function that will
calculate the length of the longest string in one of the columns of the
table. For each row, the max_len_step function is
called and passed a
After all of the rows have been processed, SQLite calls the
max_len_finalize function to determine the aggregate
result. Here, we could perform some kind of calculation based on the
data found in the
Tip
It is NOT recommended for you to store a copy of the values in the context and then process them at the end, as you would cause SQLite to use a lot of memory to process the query - just think of how much memory you would need if a million rows were stored in memory, each containing a string 32 bytes in length. Tip
You can use sqlite_create_function and sqlite_create_aggregate to override SQLite native SQL functions. See Also
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