Db/Adapter/Mysqli.php

The return value is an associative array keyed by the column name, as returned by the RDBMS. The value of each array element is an associative array with the following keys: SCHEMA_NAME => string; name of database or schema TABLE_NAME => string; COLUMN_NAME => string; column name COLUMN_POSITION => number; ordinal position of column in table DATA_TYPE => string; SQL datatype name of column DEFAULT => string; default expression of column, null if none NULLABLE => boolean; true if column can have nulls LENGTH => number; length of CHAR/VARCHAR SCALE => number; scale of NUMERIC/DECIMAL PRECISION => number; precision of NUMERIC/DECIMAL UNSIGNED => boolean; unsigned property of an integer type PRIMARY => boolean; true if column is part of the primary key PRIMARY_POSITION => integer; position of column in primary key IDENTITY => integer; true if column is auto-generated with unique values

As a convention, on RDBMS brands that support sequences (e.g. Oracle, PostgreSQL, DB2), this method forms the name of a sequence from the arguments and returns the last id generated by that sequence. On RDBMS brands that support IDENTITY/AUTOINCREMENT columns, this method returns the last value generated for such a column, and the table name argument is disregarded. MySQL does not support sequences, so $tableName and $primaryKey are ignored.