[BUG] JSQLParser 5.4 : MS SQL Server / Snowflake : ALTER TABLE t ADD a int, b int keeps only the first column, the rest becomes one UNSPECIFIC expression #2837

Failing SQL Feature:

T-SQL and Snowflake let one ADD list several columns (and, in T-SQL, table constraints) without repeating ADD. JSqlParser parses the first column correctly. Everything after the first comma ends up in a single AlterOperation.UNSPECIFIC expression whose getOptionalSpecifier() holds the rest as re-spaced raw text. There is no parse error, and simple cases deparse to the original SQL, so it goes unnoticed. Tools that walk getColDataTypeList() see only the first column.

The cause: AlterTable() splits on ,, the ADD column branch takes a single AlterExpressionColumnDataType(), and the next item (b int) only matches the captureRest() fallback in AlterExpression(). #1651 reported the same statement in 2022, back when it still threw a parse error.

SQL Example:

ALTER TABLE t ADD a int, b varchar(10) NOT NULL, c int;
ALTER TABLE t ADD a int, CONSTRAINT ck CHECK (a > 0);
ALTER TABLE t ADD COLUMN a int, b int;   -- Snowflake

Alter alter = (Alter) CCJSqlParserUtil.parse("ALTER TABLE t ADD a int, b varchar(10) NOT NULL, c int");
for (AlterExpression e : alter.getAlterExpressions()) {
    System.out.println(e.getOperation() + " | " + e.getColDataTypeList() + " | " + e.getOptionalSpecifier());
}

Actual (5.3; the grammar is the same in 5.4 and master):

ADD | [a int] | null
UNSPECIFIC | null | b varchar ( 10 ) NOT NULL , c int

The second statement gives ADD [a int] and UNSPECIFIC "CONSTRAINT ck CHECK ( a > 0 )". The third gives ADD [a int] and UNSPECIFIC "b int".

Expected: one ADD expression whose getColDataTypeList() is [a int, b varchar (10) NOT NULL, c int], as for ADD (a int, b int). For T-SQL, the CONSTRAINT ck CHECK (a > 0) item should come back as a constraint, not as raw text. Deparsing should keep the single ADD.

Software Information:

• JSqlParser 5.3 and 5.4; master as of f6ac257 has the same grammar.
• Microsoft SQL Server / Azure SQL: ADD { <column_definition> | <computed_column_definition> | <table_constraint> | <column_set_definition> } [ ,...n ], example "E. Add several columns with constraints": https://learn.microsoft.com/en-us/sql/t-sql/statements/alter-table-transact-sql
• Snowflake: "ADD COLUMN operations can be performed on multiple columns in the same command": https://docs.snowflake.com/en/sql-reference/sql/alter-table

Related: #1651, #246.