Processing of string single quotation marks in Oracle SQL and PL/SQL

In Oracle queries, single quotation marks are often added because of the string, but the location and number of single quotation marks are often difficult to grasp. Many friends have asked such questions.

Take a look at the following query, the outermost two single quotation marks are used as quotation mark operators, the second is used as escape symbols, and the random third single quote is the real data output, so the following query outputs the third single quote:

SQL > select''from dual

'

'

Further, if we wanted to put single quotation marks in the string, it would look like this:

SQL > select''YUNHE''ENMO' from dual

'' YUNHE''E

'YUNHE'ENMO

SQL > select''YUNHE''''ENMO' from dual

'' YUNHE''''

'YUNHE''ENMO

SQL > select''YUNHE''''ENMO''' from dual

'' YUNHE''''E

'YUNHE''ENMO'

In short, as long as you understand the existence of escape symbols, dealing with single quotation marks is not complicated.