MariaDB 10.2

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CREATE TABLE table1 (id int, bla1 varchar(10), bla2 varchar(10), ucr varchar(10));
INSERT INTO table1 VALUES (10001, 'ABC', 33, 'VALUE1');
INSERT INTO table1 VALUES (10002, 'DEF', 44, 'VALUE2');
CREATE TABLE table2 (id int, bla1 varchar(10), bla2 varchar(10), email varchar(100));
INSERT INTO table2 VALUES (10001, 'TYU', 33, '1@1.com');
INSERT INTO table2 VALUES (10002, 'FGT', 44, '2@2.com');
CREATE TABLE dummy (ucr int, name varchar(100), email varchar(100));
INSERT INTO dummy VALUES (10001, 'ABC', '1@1.com');
INSERT INTO dummy VALUES (10002, 'DEF', '2@2.com');
UPDATE table1
JOIN   table2 
ON     table1.id = table2.id
JOIN   dummy
ON     dummy.email = table2.email
SET    table1.ucr = dummy.ucr;
SELECT *
FROM   table1;


id
bla1
bla2
ucr


10001
ABC
33
10001

10002
DEF
44
10002