Question 1

Laravel on Postgres: duplicate key value violates unique constraint "users_pkey"

Accepted Answer

You copied rows from MySQL with their ids, but the Postgres sequence behind each id column still starts at 1. The first new insert reuses id 1, 2, 3... If your ids have gaps, it fails some inserts and not others, so it looks random. Fix: -- once per table that has a serial/identity id:
SELECT setval(pg_get_serial_sequence('users','id'),
              COALESCE((SELECT MAX(id) FROM users), 0) + 1, false);

Question 2

Laravel on Postgres: column "users.name" must appear in the GROUP BY clause or be used in an aggregate function

Accepted Answer

MySQL (with ONLY_FULL_GROUP_BY off) lets you select columns that are not grouped and returns a value from an arbitrary row. Postgres refuses. Grouping by the table's primary key is allowed, so groupBy('users.id') with users.* works. Fix: -- pick one:
SELECT team_id, MAX(name) FROM users GROUP BY team_id;          -- aggregate it
SELECT DISTINCT ON (team_id) team_id, name FROM users
  ORDER BY team_id, id DESC;                                    -- latest row per group

Question 3

Laravel on Postgres: value "3000000000" is out of range for type integer

Accepted Answer

Postgres has no unsigned integers. Laravel's unsignedInteger() and increments() become a plain integer on pgsql, so the ceiling drops from 4,294,967,295 to 2,147,483,647. Values above that loaded fine on MySQL and fail on Postgres. Fix: ALTER TABLE events ALTER COLUMN hits TYPE bigint;
-- in Laravel migrations: unsignedBigInteger() / bigIncrements() instead of
-- unsignedInteger() / increments()

Question 4

Laravel on Postgres: operator does not exist: boolean = integer

Accepted Answer

tinyint(1) columns usually become boolean on Postgres. MySQL compares them to 1/0 freely; Postgres does not when the 1 is written into the SQL text (whereRaw, DB::select with a literal, raw joins). Fix: -- raw SQL:
WHERE active = true
-- or let Laravel bind it (this works on pgsql):
->where('active', 1)

Question 5

Laravel on Postgres: operator does not exist: character varying = integer

Accepted Answer

A string column (phone, code, zip, external_id) is compared with a bare number in raw SQL. MySQL casts silently; Postgres won't guess. Fix: WHERE phone = '5551234'          -- quote it
WHERE phone = ?                  -- or bind it

Question 6

Laravel on Postgres: date/time field value out of range: "0000-00-00 00:00:00"

Accepted Answer

MySQL stores zero dates ('0000-00-00') when strict mode is off. Postgres has no such date, so the copy or the insert fails. Fix: -- on MySQL, before copying (column must allow NULL):
UPDATE orders SET shipped_at = NULL WHERE shipped_at = '0000-00-00 00:00:00';
ALTER TABLE orders MODIFY due_on date NULL DEFAULT NULL;
UPDATE orders SET due_on = NULL WHERE due_on = '0000-00-00';

Question 7

Laravel on Postgres: column "a@x.com" does not exist

Accepted Answer

If the 'column' in the error is actually a value (an email, a status word), your raw SQL uses double quotes for a string. MySQL treats "text" as a string; Postgres treats it as a column name. Fix: WHERE email = 'a@x.com'          -- single quotes for strings
WHERE email = ?                  -- or bind it

Question 8

Laravel on Postgres: syntax error at or near "`"

Accepted Answer

Backticks are MySQL-only identifier quotes. Laravel's query builder quotes for you, so these come from raw SQL: DB::statement, whereRaw, selectRaw, old migrations. Fix: SELECT * FROM users              -- no quotes
SELECT * FROM "users"            -- Postgres identifier quotes

Question 9

Laravel on Postgres: function ifnull(text, unknown) does not exist

Accepted Answer

A MySQL-only function in raw SQL. Common ones and their Postgres versions are below. Fix: IFNULL(a, b)              -> COALESCE(a, b)
GROUP_CONCAT(email)       -> string_agg(email, ',' ORDER BY id)
DATE_FORMAT(d, '%Y')      -> to_char(d, 'YYYY')
IF(cond, a, b)            -> CASE WHEN cond THEN a ELSE b END
UNIX_TIMESTAMP(d)         -> extract(epoch FROM d)
CURDATE()                 -> current_date

Question 10

Laravel on Postgres: invalid byte sequence for encoding "UTF8": 0x00

Accepted Answer

Some MySQL text values contain NUL bytes (often from binary data or bad imports). Postgres text can't store them, so the load fails. Fix: -- on MySQL, find and strip them before copying:
SELECT id FROM t WHERE INSTR(name, CHAR(0)) > 0;
UPDATE t SET name = REPLACE(name, CHAR(0), '') WHERE INSTR(name, CHAR(0)) > 0;

Question 11

Laravel on Postgres: current transaction is aborted, commands ignored until end of transaction block

Accepted Answer

This is a symptom. An earlier statement in the same transaction failed; MySQL would carry on, but Postgres refuses every statement until rollback. Code that catches an exception and keeps using the same transaction hits this. Fix: -- find the FIRST error in the log, fix that one.
-- if you must try-and-continue inside a transaction, wrap the risky step
-- in a savepoint (nested DB::transaction() does this in Laravel).

Laravel on Postgres after MySQL: paste your error