Postgres=> SELECT * FROM Test_Empty_or_Null WHERE tname IS NULL The following code is an example of the COALESCE function: Query tuning is beyond the scope of this post. In those cases, you must analyze the query run plan, revisit the indexes created, and create partial indexes if required on the table to tune the query. There are chances that your query could be slower. The database might not optimize the plan because the particular filter is changed, and any index created on such column wouldn’t be used. However, changing WHERE clauses in SQL queries to support the functionality might affect the run plan of query. You can adjust the WHERE tname IS NULL filter condition to WHERE coalesce(tname, '') = '' to get all rows whose tname is either empty or not known. ![]() NULL is returned only if all arguments are NULL. The COALESCE function returns the first of its arguments that is not NULL. ![]() Optionally, you can use NULL handling functions such as COALESCE or NULLIF in PostgreSQL to deal with scenarios containing empty strings. Postgres=> SELECT * FROM Test_Empty_or_Null WHERE tname IS NULL OR tname = '' The following is an example using Oracle : When encountering an empty string, both Oracle and PostgreSQL throw an error for multiple entries. In contrast, Oracle restricts multiple NULL instances and empty strings in a composite unique constraint or unique index. PostgreSQL allows multiple rows with NULL in unique indexes. One of the biggest differences between Oracle and PostgreSQL is how NULL and empty strings operate with regards to composite unique indexes and constraints. NULL is not comparable to anything, not even to itself, whereas empty strings can be compared.NULL = NULL results in NULL, as opposed to ” =”, which evaluates to TRUE.Finding the size or length of NULL results in NULL.It doesn’t have a value, as opposed to an empty string, which is a value but an empty one. The following conditional statements in Oracle are all evaluated to NULL:ĮRROR: invalid input syntax for type integer: ""ĮRROR: invalid input syntax for type date: "" Oracle databases treat NULL and empty strings as the same you can use empty strings and NULL interchangeably in any operation. ![]() We show examples to understand the overall components, impacts, and considerations of migration. In this post, we cover different variants of handling empty strings in PostgreSQL and viable solutions during migration. ![]() If you’re running workloads on Oracle, you might implement procedural code with business logic, assuming that empty strings are treated as NULL when performing any comparison or NULL check. However, in PostgreSQL, empty strings and NULL are different. Oracle databases treat empty strings and NULL as the same. Handling empty strings (”) with all NULL-compatible operators or expressions while migrating from Oracle to PostgreSQL is vital to achieve overall functional acceptance on the converted code and have a holistic impact. For code conversion exceptions raised by AWS SCT, we can refer to migration patterns and the Oracle to PostgreSQL migration playbook.Ĭonverting code from Oracle to a PostgreSQL-compatible engine may involve multiple corner cases that are important for your overall migration success. These services are Amazon Relational Database Service (Amazon RDS) for PostgreSQL and Amazon Aurora PostgreSQL-Compatible Edition.ĭuring the schema or code conversion phase, we can use AWS Schema Conversion Tool (AWS SCT) to convert the majority of the code. AWS offers services that make PostgreSQL database deployments easy to set up, manage, and scale for the cloud in a cost-efficient manner. An Oracle-to-PostgreSQL migration in the AWS Cloud can be a multistage process with different technologies and skills involved, starting from the assessment stage to the cutover stage.
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