Postgres 11

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CREATE TABLE t(i INT, c VARCHAR(10));

CREATE TABLE

INSERT INTO t(i,c) VALUES(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd'), (5, 'e')

INSERT 0 5

SELECT * FROM t;

i
c

1
a

2
b

3
c

4
d

5
e

SELECT 5

SELECT STRING_AGG(c ,(CASE WHEN i%2=0 THEN ' OR ' ELSE ' AND ' END)) AS r
FROM t

r

a OR b AND c OR d AND e

SELECT 1