13. A system comprising: at least one processor; and at least one memory, the at least one processor and the at least one memory configured to perform operations comprising: receiving a query for one or more data items stored in a database, wherein the query is associated with a query plan; generating a plurality of query plans for the query, the generating including: identifying at least one query operator of the query that uses data having a format different from a storage model format of at least one of the data items stored in the database; and converting the format of the data used by the at least one query operator to another format that matches the storage model format of the at least one of the data items stored in the database, wherein the plurality of query plans are based on at least a syntax of the query and an order of clauses within the query; selecting a most efficient query plan of the plurality of query plans; and executing the query using the most efficient query plan, wherein a difference between the format of the data used by the at least one query operator and the storage model format of the at least one of the data items before conversion is one of the following: the format of the data used by the at least one query operator is a row-format and the storage model format of the at least one of the data items is a column-format; or the format of the data used by the at least one query operator is the column-format and the storage model of the at least one of the data items is the row-format.
13. A system comprising: at least one processor; and at least one memory, the at least one processor and the at least one memory configured to perform operations comprising: receiving a query for one or more data items stored in a database, wherein the query is associated with a query plan; generating a plurality of query plans for the query, the generating including: identifying at least one query operator of the query that uses data having a format different from a storage model format of at least one of the data items stored in the database; and converting the format of the data used by the at least one query operator to another format that matches the storage model format of the at least one of the data items stored in the database, wherein the plurality of query plans are based on at least a syntax of the query and an order of clauses within the query; selecting a most efficient query plan of the plurality of query plans; and executing the query using the most efficient query plan, wherein a difference between the format of the data used by the at least one query operator and the storage model format of the at least one of the data items before conversion is one of the following: the format of the data used by the at least one query operator is a row-format and the storage model format of the at least one of the data items is a column-format; or the format of the data used by the at least one query operator is the column-format and the storage model of the at least one of the data items is the row-format. 16. The system of claim 13 , wherein the converting further comprises at least one of the following: converting the format of the data used by a row query operator to the column-format; or converting the format of the data used by a column query operator to the row-format.