Handling case-sensitivity with different database engines.

Most database engines have case-sensitive object identifiers. In most cases, when you do not specify identifiers in double quotes, the SQL parser automatically converts names to uppercase or lowercase, so that the identifiers match if the objects are also created without double quoted identifiers.

In ORACLE, this statement would create a table named "CUSTOMER" with a "CUST_ID" column.

This table shows the behavior of each database engine regarding case sensitivity and double quoted identifiers:

Table 1. Database server support of case sensitivity and double-quoted identifiers
Database Server Type Un-quoted names Double-quoted names
IBM® DB2® LUW Converts to uppercase Case sensitive
IBM Informix® (1) Converts to lowercase Syntax disallowed (non-ANSI mode)
Microsoft™ SQL Server (2) Not converted, kept as is Case sensitive
Oracle® MySQL / MariadDB Not converted, kept as is Syntax disallowed
Oracle Database Server Converts to uppercase Uppercase
PostgreSQL Converts to lowercase Lowercase
SAP® ASE Converts to lowercase Lowercase
SAP HANA® Converts to uppercase Case sensitive
SQLite Not converted, kept as is Case insensitive

(1) If not ANSI database mode.

(2) When case-sensitive charset/collation used.

Take care with database servers marked in red, because object identifiers are case sensitive and are not converted to uppercase or lowercase if not delimited by double-quotes. This means that, by error, you can create two tables with a similar name:
CREATE TABLE customer ( cust_id INTEGER )  -- first table 
CREATE TABLE Customer ( cust_id INTEGER )  -- second table

It is recommended to design databases with lowercase table and column names.