Use the regular expression ^( +|[A-Z '.-]*[A-Z][A-Z '.-]*)$ to match a string consisting of only either:
+
all space characters; or[A-Z '.-]*[A-Z][A-Z '.-]*
zero-or-more alphabetical or special characters then one alphabetical character and then zero-or-more alphabetical or special characters.
Like this:
Oracle Setup:
CREATE TABLE data (
value VARCHAR2(100),
CONSTRAINT value__alpha_or_special_chr CHECK ( REGEXP_LIKE( value, '^( +|[A-Z ''.-]*[A-Z][A-Z ''.-]*)$' ) )
);
Insert valid data:
INSERT INTO data ( value )
SELECT q'!ORACLE!' FROM DUAL UNION ALL
SELECT q'!ORA..C L--E!' FROM DUAL UNION ALL
SELECT q'!'''..O!' FROM DUAL UNION ALL
SELECT q'!O--...''''!' FROM DUAL UNION ALL
SELECT q'! !' FROM DUAL
Invalid data fails:
INSERT INTO data ( value )
SELECT q'!''''''''''!' FROM DUAL;
ORA-02290: check constraint (FIDDLE_TRJCYMMSYLSIPALCEYXD.VALUE__ALPHA_OR_SPECIAL_CHR) violated
INSERT INTO data ( value )
SELECT q'!--------!' FROM DUAL;
ORA-02290: check constraint (FIDDLE_TRJCYMMSYLSIPALCEYXD.VALUE__ALPHA_OR_SPECIAL_CHR) violated
INSERT INTO data ( value )
SELECT q'!ORACLE$!' FROM DUAL;
ORA-02290: check constraint (FIDDLE_TRJCYMMSYLSIPALCEYXD.VALUE__ALPHA_OR_SPECIAL_CHR) violated
INSERT INTO data ( value )
SELECT q'!ORACL#E!' FROM DUAL;
ORA-02290: check constraint (FIDDLE_TRJCYMMSYLSIPALCEYXD.VALUE__ALPHA_OR_SPECIAL_CHR) violated
Query:
SELECT * FROM data;
Output:
| VALUE |
| :----------- |
| ORACLE |
| ORA..C L--E |
| '''..O |
| O--...'''' |
| |
db<>fiddle here
