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* Add the 'Oracle-to-PostgreSQL Migration Expert' Custom Agent, its associated skills, plugin manifest * Update READMEs using 'npm run build' * Resolve PR comments: - Fix BOM characters - Rerun 'npm run build' - Clarify timestampz date kind - Remove consufing text for SELECT INTO exception - Remove dangerous VB.NET example * Update README and refcursor handling documentation for clarity and consistency * Update skills/creating-oracle-to-postgres-master-migration-plan/SKILL.md Add .slnx to discovery of projects Co-authored-by: Aaron Powell <me@aaron-powell.com> --------- Co-authored-by: TCPrimedPaul <paul.delannoy@tc.gc.ca> Co-authored-by: Aaron Powell <me@aaron-powell.com>
146 lines
4.2 KiB
Markdown
146 lines
4.2 KiB
Markdown
# Oracle to PostgreSQL: TO_CHAR() Numeric Conversions
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## Contents
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- Problem
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- Root Cause
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- Solution Patterns — CAST, format string, concatenation
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- Migration Checklist
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- Application Code Review
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- Testing Recommendations
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- Common Locations
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- Error Messages to Watch For
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## Problem
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Oracle allows `TO_CHAR()` to convert numeric types to strings without a format specifier:
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```sql
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-- Oracle: Works fine
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SELECT TO_CHAR(vessel_id) FROM vessels;
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SELECT TO_CHAR(fiscal_year) FROM certificates;
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```
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PostgreSQL requires a format string when using `TO_CHAR()` with numeric types, otherwise it raises:
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```
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42883: function to_char(numeric) does not exist
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```
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## Root Cause
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- **Oracle**: `TO_CHAR(number)` without a format mask implicitly converts the number to a string using default formatting
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- **PostgreSQL**: `TO_CHAR()` always requires an explicit format string for numeric types (e.g., `'999999'`, `'FM999999'`)
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## Solution Patterns
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### Pattern 1: Use CAST (Recommended)
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The cleanest migration approach is to replace `TO_CHAR(numeric_column)` with `CAST(numeric_column AS TEXT)`:
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```sql
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-- Oracle
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SELECT TO_CHAR(vessel_id) AS vessel_item FROM vessels;
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-- PostgreSQL (preferred)
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SELECT CAST(vessel_id AS TEXT) AS vessel_item FROM vessels;
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```
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**Advantages:**
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- More idiomatic in PostgreSQL
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- Clearer intent
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- No format string needed
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### Pattern 2: Provide Format String
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If you need specific numeric formatting, use an explicit format mask:
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```sql
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-- PostgreSQL with format
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SELECT TO_CHAR(vessel_id, 'FM999999') AS vessel_item FROM vessels;
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SELECT TO_CHAR(amount, 'FM999999.00') AS amount_text FROM payments;
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```
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**Format masks:**
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- `'FM999999'`: Fixed-width integer (FM = Fill Mode, removes leading spaces)
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- `'FM999999.00'`: Decimal with 2 places
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- `'999,999.00'`: With thousand separators
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### Pattern 3: String Concatenation
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For simple concatenation where numeric conversion is implicit:
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```sql
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-- Oracle
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WHERE TO_CHAR(fiscal_year) = '2024'
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-- PostgreSQL (using concatenation)
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WHERE fiscal_year::TEXT = '2024'
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-- or
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WHERE CAST(fiscal_year AS TEXT) = '2024'
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```
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## Migration Checklist
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When migrating SQL containing `TO_CHAR()`:
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1. **Identify all TO_CHAR() calls**: Search for `TO_CHAR\(` in SQL strings, stored procedures, and application queries
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2. **Check the argument type**:
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- **DATE/TIMESTAMP**: Keep `TO_CHAR()` with format string (e.g., `TO_CHAR(date_col, 'YYYY-MM-DD')`)
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- **NUMERIC/INTEGER**: Replace with `CAST(... AS TEXT)` or add format string
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3. **Test the output**: Verify that the string representation matches expectations (no unexpected spaces, decimals, etc.)
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4. **Update comparison logic**: If comparing numeric-to-string, ensure consistent types on both sides
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## Application Code Review
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### C# Example
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```csharp
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// Before (Oracle)
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var sql = "SELECT TO_CHAR(id) AS id_text FROM entities WHERE TO_CHAR(status) = @status";
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// After (PostgreSQL)
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var sql = "SELECT CAST(id AS TEXT) AS id_text FROM entities WHERE CAST(status AS TEXT) = @status";
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```
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## Testing Recommendations
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1. **Unit Tests**: Verify numeric-to-string conversions return expected values
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```csharp
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[Fact]
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public void GetVesselNumbers_ReturnsVesselIdsAsStrings()
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{
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var results = dal.GetVesselNumbers(certificateType);
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Assert.All(results, item => Assert.True(int.TryParse(item.DISPLAY_MEMBER, out _)));
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}
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```
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2. **Integration Tests**: Ensure queries with `CAST()` execute without errors
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3. **Comparison Tests**: Verify WHERE clauses with numeric-to-string comparisons filter correctly
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## Common Locations
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Search for `TO_CHAR` in:
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- ✅ Stored procedures and functions (DDL scripts)
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- ✅ Application data access layers (DAL classes)
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- ✅ Dynamic SQL builders
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- ✅ Reporting queries
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- ✅ ORM/Entity Framework raw SQL
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## Error Messages to Watch For
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```
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Npgsql.PostgresException: 42883: function to_char(numeric) does not exist
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Npgsql.PostgresException: 42883: function to_char(integer) does not exist
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Npgsql.PostgresException: 42883: function to_char(bigint) does not exist
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```
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## See Also
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- [oracle-to-postgres-type-coercion.md](oracle-to-postgres-type-coercion.md) - Related type conversion issues
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- PostgreSQL Documentation: [Data Type Formatting Functions](https://www.postgresql.org/docs/current/functions-formatting.html)
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