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| Original file line number | Diff line number | Diff line change |
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| @@ -1,17 +1,18 @@ | ||
| --- | ||
| title: "Demonstration of Oracle SQL compatible functions and syntax" | ||
| navTitle: "Demo: Oracle SQL compatibility" | ||
| navTitle: "Oracle SQL compatibility" | ||
| showInteractiveBadge: true | ||
| --- | ||
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| BigAnimal lets you run Oracle SQL queries in the cloud via [EDB Postgres Advanced Server](https://www.enterprisedb.com/docs/epas/latest/epas_compat_ora_dev_guide/). This topic demonstrates two Oracle SQL-syntax queries running unmodified on a BigAnimal test cluster, populated with the [Chinook sample database](https://github.com/lerocha/chinook-database). | ||
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| Watch the video, or load up psql and follow along below! | ||
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| <figure class="embed-responsive embed-responsive-16by9"> | ||
| <iframe src="https://www.youtube.com/embed/lV4QQ53kgew" | ||
| <iframe src="https://www.youtube.com/embed/lV4QQ53kgew" | ||
| title="Video recording of this demonstration" | ||
| class="embed-responsive-item" | ||
| frameborder="0" | ||
| class="embed-responsive-item" | ||
| frameborder="0" | ||
| allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> | ||
| </figure> | ||
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@@ -37,20 +38,20 @@ postgres://demo:[email protected]:54 | |
| In case you're unfamiliar with [PostgreSQL connection URIs](https://www.postgresql.org/docs/current/libpq-connect.html#id-1.7.3.8.3.6), let's break that down: | ||
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| - `demo` is the user role we're connecting as. This is a user set up with select privileges on the database. | ||
| - `password` is the password for this user. | ||
| - `password` is the password for this user. | ||
| !!! Warning Passwords in connection strings. | ||
| This example illustrates a complete connection URL, including the password. This is fine for a demonstration, | ||
| and may also be acceptable for applications configuration if access to the configuration is limited. | ||
| and may also be acceptable for applications configuration if access to the configuration is limited. | ||
| Avoid this practice for admin, superuser, or other roles used interactively - psql will prompt for a password | ||
| if none is supplied. | ||
| - `p-c64p9a3h5vfavr7tfrjg.qsbilba3hlgp1vqr.biganimal.io` is the host name for the Advanced Server cluster on BigAnimal that I'm connecting to. | ||
| if none is supplied. | ||
| - `p-c64p9a3h5vfavr7tfrjg.qsbilba3hlgp1vqr.biganimal.io` is the host name for the Advanced Server cluster on BigAnimal that I'm connecting to. | ||
| - `5432` is the usual PostgreSQL port number. | ||
| - `chinook` is the name of the database. | ||
| - `sslmode=require` ensures that we establish a secure connection. | ||
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| With that in hand, we can launch psql: | ||
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| ```shell | ||
| ```shell | ||
| psql postgres://demo:[email protected]:5432/chinook?sslmode=require | ||
| __OUTPUT__ | ||
| psql (13.0 (Debian 13.0-1.pgdg100+1), server 13.4.8 (Debian 13.4.8-1+deb10)) | ||
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@@ -86,7 +87,7 @@ __OUTPUT__ | |
| ... | ||
| ``` | ||
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| There's an employee table, let's examine its definition: | ||
| There's an employee table, let's examine its definition: | ||
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| ``` | ||
| \d+ employee | ||
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@@ -117,17 +118,17 @@ other employees who may in turn report to still *other* employees. | |
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| ## Demo #1: exposing an organization hierarchy with `CONNECT BY` | ||
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| Let's construct a [hierarchical query](https://www.enterprisedb.com/docs/epas/latest/epas_compat_ora_dev_guide/03_advanced_concepts/05_hierarchical_queries/) to expose this [chain of command](https://en.wikipedia.org/wiki/Chain_of_command). | ||
| Let's construct a [hierarchical query](https://www.enterprisedb.com/docs/epas/latest/epas_compat_ora_dev_guide/03_advanced_concepts/05_hierarchical_queries/) to expose this [chain of command](https://en.wikipedia.org/wiki/Chain_of_command). | ||
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| Modern SQL would use a recursive CTE for this, as those are widely supported. But Oracle has, for decades, supported an alternative mechanism for querying hierarchy in the form of `CONNECT BY` - let's put that into action: | ||
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| ```sql | ||
| SELECT firstname, lastname, ( | ||
| SELECT LISTAGG(lastname, ', ') | ||
| FROM employee rt | ||
| START WITH rt.employeeid=e.reportsto | ||
| SELECT LISTAGG(lastname, ', ') | ||
| FROM employee rt | ||
| START WITH rt.employeeid=e.reportsto | ||
| CONNECT BY employeeid = PRIOR reportsto | ||
| ) AS "chain of command" | ||
| ) AS "chain of command" | ||
| FROM employee e; | ||
| __OUTPUT__ | ||
| firstname | lastname | chain of command | ||
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@@ -148,11 +149,11 @@ Now, the `LISTAGG()` function was introduced in Oracle 11g Release 2. Very few d | |
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| ```sql | ||
| SELECT firstname, lastname, ( | ||
| SELECT string_agg(lastname, ', ') | ||
| FROM employee rt | ||
| START WITH rt.employeeid=e.reportsto | ||
| SELECT string_agg(lastname, ', ') | ||
| FROM employee rt | ||
| START WITH rt.employeeid=e.reportsto | ||
| CONNECT BY employeeid = PRIOR reportsto | ||
| ) AS "chain of command" | ||
| ) AS "chain of command" | ||
| FROM employee e; | ||
| __OUTPUT__ | ||
| firstname | lastname | chain of command | ||
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@@ -168,20 +169,20 @@ __OUTPUT__ | |
| (8 rows) | ||
| ``` | ||
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| But [the semantics of the two functions are different for even slightly less-trivial uses](https://www.enterprisedb.com/blog/how-workaround-oracle-listagg-function-postgresql), specifically when using the grouping construct. | ||
| But [the semantics of the two functions are different for even slightly less-trivial uses](https://www.enterprisedb.com/blog/how-workaround-oracle-listagg-function-postgresql), specifically when using the grouping construct. | ||
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| Let's demonstrate that. | ||
| Let's demonstrate that. | ||
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| ## Demo #2: group concatenation with `LISTAGG` | ||
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| As we saw above, this database has "album" and "track" tables containing metadata on digital recordings. We can use some analytic functions, including `LISTAGG`, to put together a report on average track storage requirements for albums with "baby" in the title. | ||
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| ```sql | ||
| SELECT UNIQUE title, | ||
| SELECT UNIQUE title, | ||
| ROUND(AVG(bytes) OVER (PARTITION BY mediatypeid)/1048576 ) media_avg_mb, | ||
| LISTAGG(t.name || ' (' || ROUND(bytes/1048576) || ' mb)', chr(10)) | ||
| LISTAGG(t.name || ' (' || ROUND(bytes/1048576) || ' mb)', chr(10)) | ||
| WITHIN GROUP (ORDER BY trackid) | ||
| OVER (PARTITION BY title) track_list | ||
| OVER (PARTITION BY title) track_list | ||
| FROM track t | ||
| JOIN album USING (albumid) | ||
| JOIN mediatype USING (mediatypeid) | ||
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@@ -208,11 +209,11 @@ __OUTPUT__ | |
| If we try replacing `LISTAGG` with `string_agg` in this example, it's going to fail - the [expression syntax for `string_agg`](https://www.postgresql.org/docs/current/sql-expressions.html#SYNTAX-AGGREGATES) is different. | ||
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| ```sql | ||
| SELECT UNIQUE title, | ||
| SELECT UNIQUE title, | ||
| ROUND(AVG(bytes) OVER (PARTITION BY mediatypeid)/1048576 ) media_avg_mb, | ||
| string_agg(t.name || ' (' || ROUND(bytes/1048576) || ' mb)', chr(10)) | ||
| string_agg(t.name || ' (' || ROUND(bytes/1048576) || ' mb)', chr(10)) | ||
| WITHIN GROUP (ORDER BY trackid) | ||
| OVER (PARTITION BY title) track_list | ||
| OVER (PARTITION BY title) track_list | ||
| FROM track t | ||
| JOIN album USING (albumid) | ||
| JOIN mediatype USING (mediatypeid) | ||
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@@ -225,13 +226,13 @@ LINE 3: string_agg(t.name || ' (' || ROUND(bytes/1048576) || ... | |
| HINT: No function matches the given name and argument types. You might need to add explicit type casts. | ||
| ``` | ||
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| Now, this isn't terribly difficult to correct, but it requires restructuring the query to replace the grouping construct - such work can quickly accumulate errors. Fortunately, [EDB Postgres Advanced Server](https://www.enterprisedb.com/docs/epas/latest/) | ||
| supports [`LISTAGG`](https://www.enterprisedb.com/docs/epas/latest/epas_compat_reference/02_the_sql_language/03_functions_and_operators/11_aggregate_functions/#listagg) AND `string_agg`, | ||
| Now, this isn't terribly difficult to correct, but it requires restructuring the query to replace the grouping construct - such work can quickly accumulate errors. Fortunately, [EDB Postgres Advanced Server](https://www.enterprisedb.com/docs/epas/latest/) | ||
| supports [`LISTAGG`](https://www.enterprisedb.com/docs/epas/latest/epas_compat_reference/02_the_sql_language/03_functions_and_operators/11_aggregate_functions/#listagg) AND `string_agg`, | ||
| so this query doesn't need to change when migrating from Oracle. | ||
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| ## Compatibility preserves the value of your existing work | ||
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| In both of the examples shown here, you probably would not use the functions and syntax demonstrated for new work; there are | ||
| In both of the examples shown here, you probably would not use the functions and syntax demonstrated for new work; there are | ||
| better, more familiar or at least more widely-available equivalents provided natively by PostgreSQL (and many other databases). But by supporting them, EDB Advanced Server gives you the ability to reuse existing logic with minimal modification, allowing | ||
| you to focus your time and expertise on solving new problems. | ||
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