Database Metadata¶

Table MetaData
- List the Tables in Your Database
- Determine If a Table Exists
Field MetaData

Table MetaData ¶

These functions let you fetch table information.

List the Tables in Your Database ¶

$db->listTables();

Returns an array containing the names of all the tables in the database you are currently connected to. Example:

$tables = $db->listTables();

foreach ($tables as $table)
{
        echo $table;
}

Note

Some drivers have additional system tables that are excluded from this return.

Determine If a Table Exists ¶

$db->tableExists();

Sometimes it’s helpful to know whether a particular table exists before running an operation on it. Returns a boolean TRUE/FALSE. Usage example:

if ($db->tableExists('table_name'))
{
        // some code...
}

Note

Replace table_name with the name of the table you are looking for.

Field MetaData ¶

List the Fields in a Table ¶

$db->getFieldNames()

Returns an array containing the field names. This query can be called two ways:

1. You can supply the table name and call it from the $db-> object:

$fields = $db->getFieldNames('table_name');

foreach ($fields as $field)
{
        echo $field;
}

2. You can gather the field names associated with any query you run by calling the function from your query result object:

$query = $db->query('SELECT * FROM some_table');

foreach ($query->getFieldNames() as $field)
{
        echo $field;
}

Determine If a Field is Present in a Table ¶

$db->fieldExists()

Sometimes it’s helpful to know whether a particular field exists before performing an action. Returns a boolean TRUE/FALSE. Usage example:

if ($db->fieldExists('field_name', 'table_name'))
{
        // some code...
}

Note

Replace field_name with the name of the column you are looking for, and replace table_name with the name of the table you are looking for.

Retrieve Field Metadata ¶

$db->getFieldData()

Returns an array of objects containing field information.

Sometimes it’s helpful to gather the field names or other metadata, like the column type, max length, etc.

Note

Not all databases provide meta-data.

Usage example:

$fields = $db->getFieldData('table_name');

foreach ($fields as $field)
{
        echo $field->name;
        echo $field->type;
        echo $field->max_length;
        echo $field->primary_key;
}

If you have run a query already you can use the result object instead of supplying the table name:

$query  = $db->query("YOUR QUERY");
$fields = $query->fieldData();

The following data is available from this function if supported by your database:

name - column name
max_length - maximum length of the column
primary_key - 1 if the column is a primary key
type - the type of the column

List the Indexes in a Table ¶

$db->getIndexData()

Returns an array of objects containing index information.

Usage example:

$keys = $db->getIndexData('table_name');

foreach ($keys as $key)
{
        echo $key->name;
        echo $key->type;
        echo $key->fields;  // array of field names
}

The key types may be unique to the database you are using. For instance, MySQL will return one of primary, fulltext, spatial, index or unique for each key associated with a table.

$db->getForeignKeyData()

Returns an array of objects containing foreign key information.

Usage example:

$keys = $db->getForeignKeyData('table_name');

foreach ($keys as $key)
{
        echo $key->constraint_name;
        echo $key->table_name;
        echo $key->column_name;
        echo $key->foreign_table_name;
        echo $key->foreign_column_name;
}

The object fields may be unique to the database you are using. For instance, SQLite3 does not return data on column names, but has the additional sequence field for compound foreign key definitions.