Oracle SQL

Find out who is logged in, where they connect from, and which module is running, with SYS_CONTEXT and the built-in USERENV context.

Generate random UUIDs, convert between RAW and the hyphenated text form, validate strings, and store UUIDs efficiently as RAW(16).

Compare JSON documents by their content rather than their text, and learn which differences JSON_EQUAL ignores and which it reports.

Replace, add, and delete fields of a JSON document with a merge patch, and learn why arrays are replaced whole and nulls mean delete.

Generate globally unique 16-byte identifiers for keys, use SYS_GUID as a column default, and see when a random UUID is the better choice.

Check whether a JSON document has a field or matches a filter, and pass values into path filters as variables instead of literals.

Avoid ORA-01878 in the spring gap, resolve the repeated autumn hour with TZD, and keep timestamp arithmetic correct across clock changes.

Show dates the way user interfaces do, such as 3 days ago, 6 weeks ago, or in 2 hours, directly in SQL with a long or short form.

Report by the 4-5-4 retail calendar of whole weeks, with retail month and week names and their start and end dates, without a table.

Compute fiscal years, quarters, and period start and end dates for a year that starts in April, October, or any day you choose.

Name the quarter, month, or week of a date, find the first and last day of any period, and move dates by whole periods in one call.

Group events into periods of any length, from fifteen-minute slots to six-hour blocks, by placing each timestamp in a fixed-size bucket.

Get the hours, minutes, seconds, or milliseconds between two timestamps as a number, correctly across time zones and clock changes.

Count the days, weeks, months, or years between two dates in one function, and understand why DATEDIFF counts boundaries, not whole units.

Add any unit from years to nanoseconds to a date or timestamp with DATEADD, and see how it differs from ADD_MONTHS at month ends.

Turn yes and no flags, true and false strings, and numbers into the BOOLEAN data type, with a default for values it does not recognize.

Read ISO 8601 dates and timestamps from JSON and REST services without a format model, and get the UTC time with SYS_EXTRACT_UTC.

Round exact halves to the nearest even number with banker's rounding, and keep totals of many rounded values from drifting upward.