https://docs.oracle.com/database/121/SQLRF/sql_elements001.htm#SQLRF0021 LONG Data Type

Do not create tables with LONG columns. Use LOB columns (CLOB, NCLOB, BLOB) instead. LONG columns are supported only for backward compatibility.

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Oracle also recommends that you convert existing LONG columns to LOB columns . LOB columns are subject to far fewer restrictions than LONG columns. Further, LOB functionality is enhanced in every release, whereas LONG functionality has been static for several releases. See the modify_col_properties clause of ALTER TABLE and TO_LOB for more information on converting LONG columns to LOB.

You can reference LONG columns in SQL statements in these places:

SELECT lists

SET clauses of UPDATE statements

VALUES clauses of INSERT statements

The use of LONG values is subject to these restrictions:

A table can contain only one LONG column.

You cannot create an object type with a LONG attribute.

LONG columns cannot appear in WHERE clauses or in integrity constraints (except that they can appear in NULL and NOT NULL constraints).

LONG columns cannot be indexed.

LONG data cannot be specified in regular expressions.

A stored function cannot return a LONG value.

You can declare a variable or argument of a PL/SQL program unit using the LONG data type. However, you cannot then call the program unit from SQL.

Within a single SQL statement, all LONG columns, updated tables, and locked tables must be located on the same database.

LONG and LONG RAW columns cannot be used in distributed SQL statements and cannot be replicated.

If a table has both LONG and LOB columns, then you cannot bind more than 4000 bytes of data to both the LONG and LOB columns in the same SQL statement. However, you can bind more than 4000 bytes of data to either the LONG or the LOB column.

In addition, LONG columns cannot appear in these parts of SQL statements:

GROUP BY clauses, ORDER BY clauses, or CONNECT BY clauses or with the DISTINCT operator in SELECT statements

The UNIQUE operator of a SELECT statement

The column list of a CREATE CLUSTER statement

The CLUSTER clause of a CREATE MATERIALIZED VIEW statement

SQL built-in functions, expressions, or conditions

SELECT lists of queries containing GROUP BY clauses

SELECT lists of subqueries or queries combined by the UNION, INTERSECT, or MINUS set operators

SELECT lists of CREATE TABLE ... AS SELECT statements

ALTER TABLE ... MOVE statements

SELECT lists in subqueries in INSERT statements

Triggers can use the LONG data type in the following manner:

A SQL statement within a trigger can insert data into a LONG column.

If data from a LONG column can be converted to a constrained data type (such as CHAR and VARCHAR2), then a LONG column can be referenced in a SQL statement within a trigger.

Variables in triggers cannot be declared using the LONG data type.

:NEW and :OLD cannot be used with LONG columns.

You can use Oracle Call Interface functions to retrieve a portion of a LONG value from the database.