Скачать или смотреть Solving the ORA-00905: missing keyword Error in Oracle SQL: A Deep Dive

Discover how to effectively use the `CASE` statement in Oracle SQL to avoid the `ORA-00905` error and optimize your query syntax.
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This video is based on the question https://stackoverflow.com/q/77269744/ asked by the user 'Paxman' ( https://stackoverflow.com/u/22719694/ ) and on the answer https://stackoverflow.com/a/77269758/ provided by the user 'Bohemian' ( https://stackoverflow.com/u/256196/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding and Resolving the ORA-00905: missing keyword Error

When working with SQL, especially in Oracle databases, encountering errors can be frustrating. One common issue that developers face is the ORA-00905: missing keyword error. This usually indicates that there's a syntax problem within your SQL statement, such as misuse of a CASE statement. In this guide, we will address a specific issue related to implementing a CASE statement in the WHERE clause of a query, offer a solution, and break it down for clarity.

The Problem: Using CASE in the WHERE Clause

In a recent question posed by a database developer, they attempted to use a CASE statement in the WHERE clause with a BETWEEN condition. Unfortunately, this led to the dreaded ORA-00905: missing keyword error. Let's take a closer look at the problematic SQL query:

[[See Video to Reveal this Text or Code Snippet]]

The Mistake: Misusing CASE

The key issue here is that the CASE statement is attempting to return a boolean expression directly in the WHERE clause. However, the CASE statement is designed to return a single value, not to create logical conditions.

Core Concept to Understand

CASE Statements: Designed to evaluate conditions and return a scalar value based on those conditions. They can’t return true or false directly for use in a WHERE clause.

The Solution: Restructure Your Code

To effectively avoid this error, we need to restructure the WHERE clause so that the comparison happens after the CASE returns its value. Here's how to do that:

Corrected SQL Query

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Solution

Shift the Comparison: Notice how the oc.start_date > is now placed before the CASE statement. This allows us to compare the start_date directly with the result of the CASE statement.

Maintain Logic: The logic remains intact; the only adjustment is the placement, which resolves the syntax error and ensures the query executes correctly.

Conclusion

Using CASE statements within SQL queries can be a bit tricky, but understanding their structure and purpose is key to avoiding errors like ORA-00905: missing keyword. By restructuring our WHERE clause as outlined above, we can create cleaner, more efficient queries that are less likely to cause syntax errors.

Remember, whenever you encounter a SQL error, take a moment to analyze the placement and logic of your code—often, the solution is just a slight adjustment away.

Final Thoughts

Now that you have a clearer understanding of how to handle the ORA-00905 error, you can confidently write queries that leverage CASE statements effectively. Happy querying!