Common GBase Database Migration Issues and How to Fix Them

Migrating from Oracle to GBase Database is not simply a matter of moving tables and data.

The database schema may migrate successfully while application SQL, date handling, hierarchy queries, or NULL behavior still causes problems.

The good news is that most GBase Database migration issues are predictable. If you identify them during migration assessment and test them with real application SQL, they can usually be fixed before production cutover.

This article covers four common Oracle migration issues and shows practical ways to handle them in GBase Database(GBase 8s).

Issue 1: DATE vs DATETIME Precision

One of the most common problems in an Oracle-to-GBase Database migration is date and time handling.

In Oracle, the DATE type stores both the date and time. Applications often rely on this behavior without explicitly documenting it.

For example:

-- Oracle
SELECT *
FROM orders
WHERE order_date =
      TO_DATE('2026-01-01 10:30',
              'YYYY-MM-DD HH24:MI');

During a GBase Database migration, this assumption needs to be checked.

If the application requires time precision, use an appropriate DATETIME type:

-- GBase Database
SELECT *
FROM orders
WHERE order_date =
      '2026-01-01 10:30:00'::DATETIME YEAR TO SECOND;

The important point is not simply changing the SQL syntax.

You should first identify columns that are used with:

• SYSDATE
• time comparisons
• date arithmetic
• timestamp-based filtering
• implicit string-to-date conversion

Migration tip

During a GBase Database migration assessment, review both the column definition and the SQL that accesses it.

A column named created_date may look like a date-only field, while the application may actually depend on hour, minute, or second precision.

Issue 2: ROWNUM vs LIMIT or FIRST

Oracle applications frequently use ROWNUM for result limiting:

-- Oracle
SELECT *
FROM orders
WHERE ROWNUM <= 10;

When migrating SQL to GBase Database, this Oracle-specific pattern may need to be rewritten.

For example:

-- GBase Database
SELECT FIRST 10 *
FROM orders;

Or:

SELECT *
FROM orders
LIMIT 10;

However, there is an important migration consideration: result ordering.

If the application expects the "latest 10 orders," simply replacing ROWNUM with LIMIT may not preserve the original business logic.

Prefer an explicit ordering:

SELECT *
FROM orders
ORDER BY order_date DESC
LIMIT 10;

This is a good example of why SQL compatibility should not be measured only by whether a statement can be parsed.

A successful GBase Database migration must also preserve the original query semantics.

Issue 3: Empty String vs NULL

NULL handling is another area that deserves special attention during an Oracle migration.

Oracle treats an empty string ('') as NULL in character data.

Applications may therefore contain logic such as:

SELECT *
FROM users
WHERE name IS NULL;

If the source application relies on Oracle's empty-string behavior, the same business logic may need to be reviewed when moving to GBase Database.

A defensive query may look like:

SELECT *
FROM users
WHERE name IS NULL
   OR name = '';

But don't blindly rewrite every IS NULL condition.

The correct approach is to determine whether the application considers these two states equivalent:

• value is actually NULL
• value is an empty string

This matters especially for:

• customer information
• optional fields
• status fields
• imported CSV data
• application-generated strings

Migration tip

Include NULL and empty-string cases in your GBase Database migration test data.

A schema migration can pass while application behavior changes because of a small difference in data semantics.

Issue 4: CONNECT BY and Hierarchical Queries

Oracle's CONNECT BY PRIOR is widely used for organizational structures, product categories, file trees, and other hierarchical data.

For example:

-- Oracle
SELECT *
FROM org_chart
START WITH manager_id IS NULL
CONNECT BY PRIOR id = manager_id;

When migrating to GBase Database, a recursive CTE can be used to express the hierarchy:

WITH RECURSIVE org_tree AS (
    SELECT *,
           1 AS level
    FROM org_chart
    WHERE manager_id IS NULL

    UNION ALL

    SELECT c.*,
           p.level + 1
    FROM org_chart c
    JOIN org_tree p
      ON c.manager_id = p.id
)
SELECT *
FROM org_tree
ORDER BY level, id;

The syntax is different, but the bigger issue is preserving the original hierarchy semantics.

During a GBase Database migration, check:

• root-node selection
• parent-child relationships
• recursion depth
• ordering
• duplicate paths
• cycle handling

Don't validate only whether the query executes successfully. Compare the result set with Oracle.

Don't Stop at Syntax Compatibility

These four examples highlight an important principle:

Database migration is not the same as SQL conversion.

A migration assessment should examine at least three layers.

1. SQL Syntax

Check Oracle-specific features such as:

• ROWNUM
• CONNECT BY
• proprietary functions
• Oracle hints
• implicit conversions

2. Data Semantics

Check differences involving:

• DATE
• DATETIME
• NULL
• empty strings
• numeric precision
• character data

3. Application Behavior

Check whether the application depends on:

• stored procedures
• dynamic SQL
• system packages
• transaction behavior
• error codes
• driver behavior

This is where many GBase Database migration projects discover unexpected work.

Use Tools, But Keep Human Review

Migration tools can significantly reduce manual work.

For example, GBase Database MTK can help identify and convert many migration objects and compatibility issues.

But automated conversion should be treated as the first pass, not the final validation.

Pay particular attention to:

• dynamic SQL
• complex stored procedures
• proprietary Oracle packages
• application-generated SQL
• recursive queries
• implicit type conversions

A useful workflow is:

Source Assessment
      ↓
SQL/Object Conversion
      ↓
Automated Compatibility Check
      ↓
Manual Review
      ↓
Functional Testing
      ↓
Performance Testing
      ↓
Production Cutover

This approach makes a GBase Database migration much more predictable.

A Practical GBase Database Migration Checklist

Before production cutover, verify these four areas:

• [ ] DATE and DATETIME semantics
• [ ] ROWNUM and result-limiting logic
• [ ] NULL and empty-string behavior
• [ ] CONNECT BY and hierarchical queries
• [ ] Stored procedures and dynamic SQL
• [ ] Application-generated SQL
• [ ] Query result consistency
• [ ] Performance under realistic concurrency

The goal of Oracle-to-GBase Database migration is not to make every SQL statement look identical.

The goal is to make sure the data, application behavior, query results, and performance remain correct after migration.

That is why compatibility analysis, automated migration tools, and real application testing should work together.

A successful GBase Database migration is ultimately measured by what the application does in production—not simply by how many SQL statements were converted.