Add blog on Oracle database commands

docs/blog/2020-08-28-oracle-programming/index.md

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+---
+slug: oracle-programming
+title: Programming Oracle Database
+authors: jiaqi
+tags: [Oracle, Database, JPA]
+---
+
+[//]: # (Copyright Jiaqi Liu)
+
+[//]: # (Licensed under the Apache License, Version 2.0 (the "License");)
+[//]: # (you may not use this file except in compliance with the License.)
+[//]: # (You may obtain a copy of the License at)
+
+[//]: # (    http://www.apache.org/licenses/LICENSE-2.0)
+
+[//]: # (Unless required by applicable law or agreed to in writing, software)
+[//]: # (distributed under the License is distributed on an "AS IS" BASIS,)
+[//]: # (WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.)
+[//]: # (See the License for the specific language governing permissions and)
+[//]: # (limitations under the License.)
+
+<!--truncate-->
+
+Shell
+-----
+
+### Run Oracle SQL script and Exit Afterwards
+
+```bash
+exit | sqlplus -S $user/$pwd@//$server:$port/$service_name @script.sql
+```
+
+One example value of `$service_name` could be "ORCL". Note that there is a `@` symble preceding the script
+path(`script.sql`)
+
+### Connecting to Oracle DB Instance From the Command Line
+
+#### (First Time) Install Oracle Instant Client and sqlplus using Homebrew
+
+1. Download the two files below from [here](http://www.oracle.com/technetwork/topics/intel-macsoft-096467.html). This
+   is necessary because of Oracle licenses:
+
+   - `instantclient-basic-macos.x64–<version>.zip`
+   - `instantclient-sqlplus-macos.x64–<version>.zip`
+
+2. Run
+
+```bash
+brew tap InstantClientTap/instantclient
+brew install instantclient-basic
+brew install instantclient-sqlplus
+```
+
+#### Connect
+
+```bash
+sqlplus ${DBUSER}/${DBUSERPASSWORD}@//${HOST}:${PORT}/${SERVICE_NAME}
+```
+
+where `SERVICE_NAME` is the same thing as "database name" as in MySQL terminology
+
+### Shell Commands
+
+#### Display UTF8
+
+Whenever a client program (such as `sqlplus`) connects to the database, it tells the database what characterset it is
+using. Some environments may have a very restricted characterset and use something like US7ASCII so they don't get
+anything that can upset them.
+
+As you can see in the following example, what is output by a query is dependent on the NLS_LANG setting of a client.
+
+```shell
+C:\>set NLS_LANG=.US7ASCII
+C:\>sqlplus ???/???@xe
+
+SQL*Plus: Release 10.2.0.1.0 - Production on Wed Nov 3 09:31:32 2010
+> select chr(193) from dual;
+
+C
+-
+?
+
+> quit
+
+C:\>set NLS_LANG=.AL32UTF8
+C:\>sqlplus ???/???@xe
+
+SQL*Plus: Release 10.2.0.1.0 - Production on Wed Nov 3 09:31:49 2010
+> select chr(193) from dual;
+
+C
+-
+┴
+```
+
+If your client is Windows, then try the above. If it is a unix(ish) platform, try
+
+```bash
+export NLS_LANG=.AL32UTF8
+```
+
+#### Spool SQL Query Output to HTML format in SQLPLUS Oracle
+
+In SQLPLUS:
+
+```sql
+set pages 500
+SET MARKUP HTML ON
+spool report1.html
+Select * from hr.departments where department_id < 20;
+spool off
+```
+
+This would generate a "report1.html" file in the directory where SQLPLUS command was invoked and the file looks like
+the following:
+
+![Error loading sqlplus-html.png](./sqlplus-html.png)
+
+#### Show Tables
+
+If you have worked with MySQL, you may be familiar with the `SHOW TABLES` command that lists all tables in a database:
+
+```sql
+SHOW TABLES;
+```
+
+Unfortunately, Oracle **does not** directly support the `SHOW TABLES` command. However, you can list all tables in a
+database by querying from various data dictionary views.
+
+##### Show Tables Owned By the Current User
+
+To show tables **owned** by the current user, you query from the `user_tables` view.
+
+```sql
+SELECT table_name
+FROM user_tables
+ORDER BY table_name;
+```
+
+Note that this view does not show the `OWNER` column. Also, the user_tables table **does not** contain the other tables
+that are **accessible** by the current user.
+
+##### Show Tables Accessible By the Current User
+
+To show all tables that are currently **accessible** by the current user, regardless of owners, you query from the
+`all_tables` view:
+
+```sql
+SELECT table_name
+FROM all_tables
+ORDER BY table_name;
+```
+
+If you want to show all tables of a specific owner, you add the `OWNER` column in the `WHERE` clause as shown in the
+following query:
+
+```sql
+SELECT *
+FROM all_tables
+WHERE OWNER = 'OT'
+ORDER BY table_name;
+```
+
+##### Show All Tables in the Oracle Database
+
+To show **all tables** in the entire Oracle Database, you query from the `dba_tables` view as follows:
+
+```sql
+SELECT table_name
+FROM dba_tables;
+```
+
+You will get the following error message if you don't have access to the `dba_tables` view:
+
+```bash
+ORA-00942: table or view does not exist
+```
+
+In this case, you should request your database administrator to grant your account either privileges on the `dba_tables`
+view, or `SELECT ANY DICTIONARY` privilege, or `SELECT_CATALOG_ROLE` privilege.
+
+#### [Comparing Dates](https://stackoverflow.com/a/34061999)
+
+```sql
+Select count(*) From Employee
+Where to_char(employee_date_hired, 'YYYMMMDDD') > 19940620
+```
+
+or
+
+```sql
+Select count(*) From Employee
+employee_date_hired > TO_DATE('20-06-1994', 'DD-MM-YYYY');
+```
+
+#### [Show Last Command Run](https://stackoverflow.com/a/51193086)
+
+The 'l' command will show the last run command
+
+```sql
+SQL> l
+    1* select owner, count(1) from dba_tables group by owner
+SQL>
+```
+
+To get more than that, turn on history
+
+```sql
+SQL> set history on
+SQL> history
+  1  select * from dual;
+  2  select sysdate from dual;
+  3  show history
+```
+
+#### [Get A List of All Tables](https://stackoverflow.com/a/205746)
+
+```sql
+SELECT OWNER, TABLE_NAME
+FROM DBA_TABLES;
+```
+
+This is assuming that you have access to the `DBA_TABLES` data dictionary view. If you do not have those privileges but
+need them, you can request that the DBA explicitly grants you privileges on that table, or, that the DBA grants you the
+`SELECT ANY DICTIONARY` privilege or the `SELECT_CATALOG_ROLE` role (either of which would allow you to query any data
+dictionary table). Of course, you may want to exclude certain schemas like `SYS` and `SYSTEM` which have large numbers
+of Oracle tables that you probably don't care about.
+
+Alternatively, if you do not have access to `DBA_TABLES`, you can see all the tables that your account has access to
+through the `ALL_TABLES` view:
+
+```sql
+SELECT OWNER, TABLE_NAME
+FROM ALL_TABLES;
+```
+
+Although, that may be a subset of the tables available in the database (`ALL_TABLES` shows you the information for all
+the tables that your user has been granted access to).
+
+If you are only concerned with the tables that you own, not those that you have access to, you could use `USER_TABLES`:
+
+```sql
+SELECT TABLE_NAME
+FROM USER_TABLES;
+```
+
+Since `USER_TABLES` only has information about the tables that you own, it does not have an `OWNER` column - the owner,
+by definition, is you.
+
+Oracle also has a number of legacy data dictionary views -- `TAB`, `DICT`, `TABS`, and `CAT` for example -- that could
+be used. In general, I would not suggest using these legacy views unless you absolutely need to backport your scripts to
+Oracle 6. Oracle has not changed these views in a long time so they often have problems with newer types of objects. For
+example, the `TAB` and `CAT` views both show information about tables that are in the user's recycle bin while the
+`[DBA|ALL|USER]_TABLES` views all filter those out. `CAT` also shows information about materialized view logs with a
+`TABLE_TYPE` of "TABLE" which is unlikely to be what you really want. `DICT` combines tables and synonyms and doesn't
+tell you who owns the object.
+
+Scripting
+---------
+
+### WHENEVER SQLERROR
+
+When you have a script that has syntax errors, the script won't exit with error while executing the line that has the
+syntax error. We would like to, instead, halt the execution at that point for the script tuning purposes. To do that
+`WHENEVER SQLERROR` could be used.
+
+The commands in the following script cause SQL*Plus to exit and return the SQL error code if the SQL UPDATE command
+fails:
+
+```sql
+WHENEVER SQLERROR EXIT SQL.SQLCODE
+UPDATE EMP_DETAILS_VIEW SET SALARY = SALARY*1.1;
+```
+
+### Drop All User Tables
+
+```sql
+BEGIN
+   FOR cur_rec IN (SELECT object_name, object_type
+                   FROM user_objects
+                   WHERE object_type IN
+                             ('TABLE',
+                              'VIEW',
+                              'MATERIALIZED VIEW',
+                              'PACKAGE',
+                              'PROCEDURE',
+                              'FUNCTION',
+                              'SEQUENCE',
+                              'SYNONYM',
+                              'PACKAGE BODY'
+                             ))
+   LOOP
+      BEGIN
+         IF cur_rec.object_type = 'TABLE'
+         THEN
+            EXECUTE IMMEDIATE 'DROP '
+                              || cur_rec.object_type
+                              || ' "'
+                              || cur_rec.object_name
+                              || '" CASCADE CONSTRAINTS';
+         ELSE
+            EXECUTE IMMEDIATE 'DROP '
+                              || cur_rec.object_type
+                              || ' "'
+                              || cur_rec.object_name
+                              || '"';
+         END IF;
+      EXCEPTION
+         WHEN OTHERS
+         THEN
+            DBMS_OUTPUT.put_line ('FAILED: DROP '
+                                  || cur_rec.object_type
+                                  || ' "'
+                                  || cur_rec.object_name
+                                  || '"'
+                                 );
+      END;
+   END LOOP;
+   FOR cur_rec IN (SELECT *
+                   FROM all_synonyms
+                   WHERE table_owner IN (SELECT USER FROM dual))
+   LOOP
+      BEGIN
+         EXECUTE IMMEDIATE 'DROP PUBLIC SYNONYM ' || cur_rec.synonym_name;
+      END;
+   END LOOP;
+END;
+/
+```
+
+Troubleshooting
+---------------
+
+### Double Quotes v.s. Single Quotes
+
+Unlike MySQL which makes double and single quotes interchangeable.
+
+### Oracle: ORA-00955: name is already used by an existing object
+
+#### Cause 1
+
+You probably have another object with the same name, for example, 'person'
+
+You can find it by quering `person`:
+
+```sql
+SELECT * FROM user_objects WHERE object_name = 'person';
+```
+
+Then drop it (replace `TYPE_OF_OBJECT` by the type of the object from the above query):
+
+```sql
+DROP TYPE_OF_OBJECT person
+```
+
+#### Cause 2
+
+You simply have a stupid `/` at the end of your statement, such as
+
+```sql
+CREATE TABLE some_schema.person (
+    ...
+);
+/
+```
+
+Note the `/` at the end of the query statement
+
+### ORA-02261: such unique or primary key already exists in the table
+
+You simply have a stupid `/` at the end of your statement, such as
+
+```sql
+CREATE TABLE BRANCH(
+BRA_CODE NUMBER NOT NULL PRIMARY KEY,
+BRA_NAME VARCHAR(15),
+BRA_ADDR VARCHAR(30),
+ CITY_ID NUMBER);
+
+ALTER TABLE BRANCH ADD CONSTRAINT UNIQUE_BRANCH_NAME UNIQUE (BRA_NAME);
+\
+```
+
+Note the `/` at the end of the query statement
+
+### Change varchar Column to CLOB
+
+Given that the operation of moving from a varchar column to a CLOB is disallowed, the most straightforward way would be
+to create a new column and move the data from the old column to the new column:
+
+```sql
+ALTER TABLE atable ADD (tmpdetails  CLOB);
+UPDATE atable SET tmpdetails=details;
+COMMIT;
+ALTER TABLE atable DROP COLUMN details;
+ALTER TABLE atable RENAME COLUMN tmpdetails TO details;
+```