Question

I am using MySql, JDBC, Java to make my code. I am unable to understand what some terms in the API mean. It is preventing me from doing the work below-
To make code that checks if a particular DB exists, then checks if a particular table DB exists in that DB, followed by a particular column in that table.

Each table description has the following columns:

TABLE_CAT String => table catalog (may be null)
TABLE_SCHEM String => table schema (may be null)
TABLE_NAME String => table name
TABLE_TYPE String => table type. Typical types are "TABLE", "VIEW", "SYSTEM     TABLE",     "GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM".
REMARKS String => explanatory comment on the table
TYPE_CAT String => the types catalog (may be null)
TYPE_SCHEM String => the types schema (may be null)
TYPE_NAME String => type name (may be null)
SELF_REFERENCING_COL_NAME String => name of the designated "identifier" column of a typed table (may be null)
REF_GENERATION String => specifies how values in SELF_REFERENCING_COL_NAME are  created.      
Values are "SYSTEM", "USER", "DERIVED". (may be null)

What is a table catalog, what is a table schema, SELF_REFERENCING_COL_NAME etc ?

Answer 1

As far as Connector/J implementation of DatabaseMetadata is concerned TABLE_CAT returns the database name (as in CREATE DATABASE); TABLE_SCHEM is null and SELF_REFERENCING_COL_NAME is not returned.

This is database and driver specific. As an example, Oracle ojdbc drivers will return null for TABLE_CAT and the object owner for TABLE_SCHEM.

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For your particular task (MySQL + Connector/J):

1. To check if a particular database exists → Use getCatalogs() to obtain a ResultSet, iterate its rows and retrieve the TABLE_CAT column, your database should match one of its values.
2. To check if the database contains a particular table → getTables(databaseName, null, tableName, new String[]{"TABLE"}) should return a non empty ResultSet.
3. To check if the table contains a particular column → getColumns(databaseName, null, tableName, columnName) should return a non empty ResultSet.