By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
SELECT TRUNC(sysdate, 'MM') FROM DUAL;
| TRUNC(SYSDATE,'MM') |
|---|
| 01-APR-19 |
SELECT TRUNC(sysdate) - TO_NUMBER(TO_CHAR(sysdate,'DD')) + 1 FROM dual
| TRUNC(SYSDATE)-TO_NUMBER(TO_CHAR(SYSDATE,'DD'))+1 |
|---|
| 01-APR-19 |
SELECT ADD_MONTHS((LAST_DAY(sysdate)+1),-1) FROM DUAL;
| ADD_MONTHS((LAST_DAY(SYSDATE)+1),-1) |
|---|
| 01-APR-19 |