Postgres 13

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CREATE TABLE "Users" (
    id bigserial PRIMARY KEY,
    "onboardedAt" timestamp with time zone,
    "closedAt" timestamp with time zone
);

CREATE TABLE "Transactions" (
    id bigserial PRIMARY KEY,
    "userId" bigint,
    "createdAt" timestamp with time zone,
    amount numeric(20,8) NOT NULL DEFAULT 0
);

CREATE TABLE "UserActions" (
    id bigserial PRIMARY KEY,
    "userId" bigint,
    "createdAt" timestamp with time zone,
    action character varying(255) NOT NULL
);

INSERT INTO "Users" ("onboardedAt", "closedAt") VALUES 
    ( '2021-01-01', '2021-02-01' ), 
    ( '2021-01-01', '2021-02-01' ), 
    ( '2021-01-01', '2021-02-01' ), 
    ( '2021-02-01', '2021-03-01' ), 
    ( '2021-02-01', '2021-03-01' );

INSERT INTO "Transactions" ("userId", "createdAt", "amount") VALUES 
    ( 1, '2021-01-02',  100 ), 
    ( 1, '2021-01-08', -100 ), 
    ( 1, '2021-01-15', -200 ),
    ( 1, '2021-01-22',  200 ),

( 2, '2021-01-02', -100 ), 
    ( 2, '2021-01-02',  100 ), 
    ( 2, '2021-01-15', -200 ),
    ( 2, '2021-01-16',  200 ),

( 3, '2021-01-02',  100 ), 
    ( 3, '2021-01-08', -100 ), 
    ( 3, '2021-01-15', -200 ),
    ( 3, '2021-01-22',  200 ),

( 4, '2021-02-02',   50 ), 
    ( 4, '2021-02-08', -100 ), 
    ( 4, '2021-02-15', -200 ),
    ( 4, '2021-02-22',  200 ),

( 5, '2021-02-02',  200 ), 
    ( 5, '2021-02-08', -400 ), 
    ( 5, '2021-02-15', -600 ),
    ( 5, '2021-02-22',  200 );

INSERT INTO "UserActions" ("userId", "createdAt", "action") VALUES 
    ( 1, '2021-01-01', 'PLAY' ), 
    ( 1, '2021-01-01', 'PLAY' ), 
    ( 1, '2021-01-02', 'DEPOSIT' ), 
    ( 1, '2021-01-08', 'DEPOSIT' ), 
    ( 1, '2021-01-09', 'PLAY' ), 
    ( 1, '2021-01-15', 'PLAY' ), 
    ( 1, '2021-01-22', 'PLAY' ),

( 2, '2021-01-01', 'PLAY' ), 
    ( 2, '2021-01-01', 'PLAY' ), 
    ( 2, '2021-01-02', 'DEPOSIT' ), 
    ( 2, '2021-01-08', 'DEPOSIT' ), 
    ( 2, '2021-01-09', 'PLAY' ), 
    ( 2, '2021-01-15', 'PLAY' ), 
    ( 2, '2021-01-22', 'PLAY' ),

( 3, '2021-01-01', 'PLAY' ), 
    ( 3, '2021-01-01', 'PLAY' ), 
    ( 3, '2021-01-02', 'DEPOSIT' ), 
    ( 3, '2021-01-08', 'DEPOSIT' ), 
    ( 3, '2021-01-09', 'PLAY' ), 
    ( 3, '2021-01-15', 'PLAY' ), 
    ( 3, '2021-01-22', 'PLAY' ),

( 4, '2021-02-01', 'DEPOSIT' ), 
    ( 4, '2021-02-01', 'PLAY' ), 
    ( 4, '2021-02-02', 'DEPOSIT' ), 
    ( 4, '2021-02-08', 'DEPOSIT' ), 
    ( 4, '2021-02-09', 'PLAY' ), 
    ( 4, '2021-02-15', 'PLAY' ), 
    ( 4, '2021-02-22', 'PLAY' ),

( 5, '2021-02-01', 'DEPOSIT' ), 
    ( 5, '2021-02-01', 'PLAY' ), 
    ( 5, '2021-02-02', 'PLAY' ), 
    ( 5, '2021-02-08', 'PLAY' ), 
    ( 5, '2021-02-09', 'PLAY' ), 
    ( 5, '2021-02-15', 'DEPOSIT' ), 
    ( 5, '2021-02-22', 'PLAY' );

CREATE TABLE

CREATE TABLE

CREATE TABLE

INSERT 0 5

INSERT 0 20

INSERT 0 35

SELECT user_id, "onboardedAt", "closedAt", week_start, tx_count
     , last_user_action AS last_user_action_with_null
     , COALESCE(last_user_action, max(last_user_action) OVER (PARTITION BY user_id, null_grp)) AS last_user_action
FROM  (
   SELECT id AS user_id, u."onboardedAt", u."closedAt"
        , week_start, COALESCE(t.tx_count, 0) AS tx_count, a.last_user_action
        , count(a.last_user_action) OVER (PARTITION BY id ORDER BY week_start) AS null_grp
   FROM   "Users" u
   CROSS  JOIN  generate_series(date_trunc('week', u."onboardedAt"), u."closedAt", interval '1 week') AS week_start
   LEFT   JOIN (
      SELECT "userId" AS id, date_trunc('week', t."createdAt") AS week_start, count(*) AS tx_count
      FROM   "Transactions" t
      GROUP  BY 1, 2
      ) t  USING (id, week_start)
   LEFT   JOIN (
      SELECT DISTINCT ON (1, 2)
             "userId" AS id, date_trunc('week', a."createdAt") AS week_start, action AS last_user_action
      FROM   "UserActions" a
      ORDER  BY 1, 2, "createdAt" DESC
      ) a USING (id, week_start)
   ) sub
ORDER  BY user_id, week_start;

user_id	onboardedAt	closedAt	week_start	tx_count	last_user_action_with_null	last_user_action
1	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2020-12-28 00:00:00+00	1	DEPOSIT	DEPOSIT
1	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-04 00:00:00+00	1	PLAY	PLAY
1	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-11 00:00:00+00	1	PLAY	PLAY
1	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-18 00:00:00+00	1	PLAY	PLAY
1	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-25 00:00:00+00	0	null	PLAY
1	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-02-01 00:00:00+00	0	null	PLAY
2	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2020-12-28 00:00:00+00	2	DEPOSIT	DEPOSIT
2	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-04 00:00:00+00	0	PLAY	PLAY
2	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-11 00:00:00+00	2	PLAY	PLAY
2	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-18 00:00:00+00	0	PLAY	PLAY
2	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-25 00:00:00+00	0	null	PLAY
2	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-02-01 00:00:00+00	0	null	PLAY
3	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2020-12-28 00:00:00+00	1	DEPOSIT	DEPOSIT
3	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-04 00:00:00+00	1	PLAY	PLAY
3	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-11 00:00:00+00	1	PLAY	PLAY
3	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-18 00:00:00+00	1	PLAY	PLAY
3	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-01-25 00:00:00+00	0	null	PLAY
3	2021-01-01 00:00:00+00	2021-02-01 00:00:00+00	2021-02-01 00:00:00+00	0	null	PLAY
4	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-01 00:00:00+00	1	DEPOSIT	DEPOSIT
4	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-08 00:00:00+00	1	PLAY	PLAY
4	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-15 00:00:00+00	1	PLAY	PLAY
4	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-22 00:00:00+00	1	PLAY	PLAY
4	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-03-01 00:00:00+00	0	null	PLAY
5	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-01 00:00:00+00	1	PLAY	PLAY
5	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-08 00:00:00+00	1	PLAY	PLAY
5	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-15 00:00:00+00	1	DEPOSIT	DEPOSIT
5	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-02-22 00:00:00+00	1	PLAY	PLAY
5	2021-02-01 00:00:00+00	2021-03-01 00:00:00+00	2021-03-01 00:00:00+00	0	null	PLAY

SELECT 28